共查询到20条相似文献,搜索用时 365 毫秒
1.
Movement of natural sand particles (d=200−300 μm) in a simulated atmospheric boundary layer was visualized using a digital
high-speed camera. The consecutive particle images recorded at 2000 fps (frame per second) enabled us to observe the particle
transport in detail, especially near the flat sand surface. Various modes of sand saltation were identified. The transverse
motion of particles, often ignored in previous studies, was also visualized. In addition, instantaneous velocity fields of
saltating particles were obtained using a particle tracking velocimetry (PTV), and statistical analysis of saltating particle
trajectories was performed. The qualitative and quantitative results of the present study will be useful for understanding
the basic physics of transport of saltating sand particles. 相似文献
2.
Albert?Mihranyan Mortadha?Muhel Maria?Str?mme 《Applied Physics A: Materials Science & Processing》2009,94(2):299-305
The dissolution process of sparingly soluble CaCO3 microparticles and how the fractal surface dimension of the particles changes during dissolution is analyzed. The particles
and the dissolution process are studied using scanning electron microscopy, X-ray diffraction, nitrogen adsorption, laser
diffraction and conductance measurements. Ball milling of the particles is shown to maintain the particle crystallinity, and
to introduce an increased fractal surface dimension in the 1–10 μm size range. Dissolution is found to increase the surface
dimension of initially smooth particles and to maintain the fractal surface roughness of milled particles. The dissolution
process increases the relative number of small particles (50 nm–1 μm) whereas the larger ones decrease in size. The solubility
of the milled fractal particles was ∼1.8 times higher than that for the initially smooth ones. The presented findings show
that developing methods for increasing the fractal surface roughness of particles should be of interest for improving the
solubility of poorly soluble drug candidates. 相似文献
3.
4.
T. A. Alekhova V. Ya. Shklover N. A. Zagustina N. V. Shvyndina A. D. Plotnikov A. L. Vasil’ev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(5):747-753
The surfaces of AMg6 (aluminum-magnesium) alloy samples that have passed accelerated biocorrosion tests have been investigated
in a Quanta-3D scanning electron microscope. The alloy samples have been treated with the Ulocladium botrytis Preuss fungus, which is an active destructive fungus and was previously extracted on surfaces of the International Space Station.
Biocorrosion pits 2–10 μm in diameter, cavities the depths of which can reach 70–250 μm depth, and spots of modified color
are found to be the most typical defects. The surfaces of large cavities consist of faceted cubic particles that are formed
when the acid products of fungus metabolism interact with the alloy surface. The particles have an average size of 30 μm,
which is close to the size of alloy grains. The microstructure of a biocorrosion layer has been investigated in a Quanta-3D
microscope with the use of a focused Ga+ ion beam. The samples of 12-μm-wide transverse slices are obtained near large cavities and investigated in a Tecnai G230ST transmission electron microscope. The X-ray microanalysis of the defective layer has revealed the high concentration of
oxygen in this layer. Obtained images indicate that the corrosion cavity surface has a complex porous structure. 相似文献
5.
G. Fuhr C. Reichle T. Müller K. Kahlke K. Schütze M. Stuke 《Applied Physics A: Materials Science & Processing》1999,69(6):611-616
An electric cage-laser micro-turning lathe was realised and applied to contact-free handling and mechanical processing of
micro particles. Since particles with diameters of several micrometers cannot be fixed in mechanical chucks, an octode field
cage was used to trap and rotate a single particle in a fluid without any mechanical surface contact. A pulsed nitrogen laser
of high beam quality focused to about 1 μm in diameter could be adjusted independently of the cage position. The trapping
forces (negative dielectrophoresis) acting on a bead of 5 to 15 μm are up to several hundred pN. This and the surrounding
fluid damp down the effect of the laser pulses during bead processing. Examples demonstrating the possibilities of this technique
are shown. Microsystems with high optical quality were fabricated photolithographically or by laser direct-write chemical
vapor deposition (LCVD). Technical and biotechnological applications are discussed.
Received: 20 October 1999 / Accepted: 27 October 1999 / Published online: 10 November 1999 相似文献
6.
T. Müller A. M. Gerardino T. Schnelle S. G. Shirley G. Fuhr G. De Gasperis R. Leoni F. Bordoni 《Il Nuovo Cimento D》1995,17(4):425-432
Summary Four e-beam-processed, planar electrodes with gaps between 0.5 and 4 μm were used to create quadrupole electric-field trap.
The electrodes were immersed in an aqueous particle suspension and driven by kHz to MHz signals of several volts amplitude.
Micron and submicron particles could be stably trapped by negative dielectrophoresis. Latex beads of 1000, 600, 100 and 14
nm diameter could be concentrated between the electrodes (positive dielectrophoresis) or levitated as condensed cloud (negative
dielectrophoresis). The results are surprising since polarisation forces depend on the volume of the particle and, up to now,
it was expected that thermal forces would dominate the behaviour of particles with diameters <100 nm. However, micron-scaled
electrode configurations allow the application of extremely strong fields (up to 20 MV/m) and open up new perspectives for
microparticle handling and macromolecule trapping. 相似文献
7.
B. Denker B. Galagan V. Osiko S. Sverchkov E. Dianov 《Applied physics. B, Lasers and optics》2007,87(1):135-137
A new Bi-doped boro-alumino-phosphate glass (BAP) composition was developed. Absorption and emission spectra and luminescence
decay kinetics were investigated. The emission spectrum consists of two wide bands in the visible (0.6–0.8 μm) and near-infrared
(∼1.0–1.5 μm) ranges. The luminescence decay curve investigation has revealed a complicated behavior dependent on both excitation
and registration wavelengths. In contrast to earlier investigated Bi-doped glasses, Bi:BAP has good technological properties
and can be easily scaled. This makes the developed glass composition interesting for broadband tunable (∼1.0–1.5 μm) lasers
and amplifiers.
PACS 32.70.Cs; 78.20.-e; 78.55.Qr 相似文献
8.
Second harmonic generation (SHG) spectroscopy is a recently developed technique for the investigation of surface properties
of particles. To apply the method to technical colloidal systems, the dependences of several experimental parameters on the
signal have to be studied. In this work the influence of particle concentration on the SHG signal from the surfaces of colloids
(polystyrene beads in a size range of 0.1 μm to 2.9 μm) is investigated. A simple model, based on Lambert–Beer’s law, to describe
the measured dependences is derived. The model agrees with the experimental observations for particles smaller 1.1 μm and
with a small modification also for larger particles. Based on the new model an analytical equation for determining the optimum
concentration, where highest signals in colloidal SHG spectroscopy measurements are obtained, is derived.
PACS 42.25.Fx; 42.65.-k; 82.70.Dd 相似文献
9.
V. V. Zalamai V. V. Ursaki C. Klingshirn H. Kalt G. A. Emelchenko A. N. Redkin 《Applied physics. B, Lasers and optics》2009,97(4):817-823
A vertically arranged nearly parallel array of ZnO nanorods and randomly oriented nanowires has been grown by low pressure
chemical vapor deposition (CVD) on silica substrates and on stainless steel gauze woven from a wire with a diameter of 40 μm,
respectively. The quality of the produced material is high enough to act as a gain medium for stimulated emission in the ultraviolet
spectral region. Multiple sharp lasing peaks were realized from single hexagonal nanorods and arrays of hexagonal ZnO nanorods.
The lasing peaks display successive onset and saturation with increasing excitation power density and fit well the expected
resonance spectrum of guided modes in hexagonal nanorods. The behavior of lasing spectra from shot to shot of pumping in randomly
oriented nanowires along with the independence of the lasing threshold on the excitation spot area suggest that the emission
spectrum results from the superposition of lasing modes in individual nanowires, rather than from random lasing due to photon
coherent scattering. 相似文献
10.
We present observations of sub-micron- to micron-sized particles generated by high fluence (≈2 J/cm2) 248-nm laser ablation of pressed polytetrafluorethylene (PTFE) targets in air at atmospheric pressure. The original target
material was hydrostatically compressed ≈7 μm PTFE powder, sintered at 275 °C. Collected ejecta due to laser irradiation consists
of four basic particle morphologies ranging from small particles 50–200 nm in diameter to larger particles ≈10 μm in diameter.
Many particles formed in air carry electric charge. Using charged electrodes we are able to collect charged particles to determine
relative numbers of ± charge. We observe roughly equal numbers of positively and negatively charged particles except for the
largest particles which were predominantly negative. For a range of particle sizes we are able to measure the sign and magnitude
of this charge with a Millikan-oil-drop technique and determine surface charge densities. The implications of these observations
with respect to pulsed laser deposition of PTFE thin films and coatings are discussed.
Received: 15 January 1999 / Accepted: 18 January 1999 / Published online: 7 April 1999 相似文献
11.
H. G. Häfele 《Applied Physics A: Materials Science & Processing》1974,5(2):97-108
The properties of the spin-flip Raman laser (SFR laser) which depend on stimulated Raman scattering from mobile conduction
electrons in InSb under an external magnetic field are presented. The essential parameters are derived from a macroscopic
treatment of the stimulated Raman effect and the microscopic theory of the scattering cross-section, and are compared with
experimental results. Output pulse powers as large as 1 kW have been measured for 10.6 and 5.3 μm excitation radiation and
continuous powers of 1 W for continuous excitation with a 5.3 μm pump source. The SFR laser offers some interesting applications
in physics and chemistry, since its frequency is proportional to the applied magnetic field and its linewidth can be made
smaller than 1 kHz. 相似文献
12.
M. S. Gaponenko K. V. Yumashev A. A. Onushchenko 《Journal of Applied Spectroscopy》2010,77(5):663-667
Luminescence of lead sulfide (PbS) nanocrystals with mean diameter 6 nm in a silicate glass matrix that emit in wavelength
region 1.5 μm (0.827 eV) is studied. The average luminescence decay time is estimated to be 2.7 μs. Decreasing the temperature
is shown to result in a shift of the emission spectrum to lower energies with a corresponding temperature coefficient of 64
μeV/K. Anti-Stokes luminescence of the PbS nanocrystals is detected with a spectral shift of 45 meV for the emission band
maximum relative to the excitation energy. 相似文献
13.
Whispering gallery mode (WGM) based micro-optical sensors are known to have higher sensitivity than fiber Bragg grating, Fabry–Perot,
and microbend sensors. WGM sensors are created by optical coupling of a dielectric microparticle with an optical fiber. The
combination of a microparticle and an optical-fiber to create the sensor requires encapsulating them in a suitable material
so that the sensor can be used in practical applications. The sensitivity of the encapsulated sensors needs to be calibrated
before they can be used. The present study conducts a parametric study to understand the effect of variables such as particle
size and particle–fiber distance on the sensitivity of the encapsulated WGM sensors. Solid and hollow microparticle based
sensors are studied. In the case of hollow particles, their wall thickness effects are also characterized. Results show that
despite small strain, change in the index of refraction of the particle material due to the applied force contributes significantly
in determining the sensitivity of these sensors. 相似文献
14.
Otto?H?nninen Irene?Brüske-Hohlfeld Miranda?Loh Tobias?Stoeger Wolfgang?Kreyling Otmar?Schmid Annette?Peters 《Journal of nanoparticle research》2010,12(1):91-99
Several studies have reported laser printers as significant sources of nanosized particles (<0.1 μm). Laser printers are used
occupationally in office environments and by consumers in their homes. The current work combines existing epidemiological
and toxicological evidence on particle-related health effects, measuring doses as mass, particle number and surface area,
to estimate and compare the potential risks in occupational and consumer exposure scenarios related to the use of laser printers.
The daily uptake of laser printer particles was estimated based on measured particle size distributions and lung deposition
modelling. The obtained daily uptakes (particle mass 0.15–0.44 μg d−1; particle number 1.1–3.1 × 109 d−1) were estimated to correspond to 4–13 (mass) or 12–34 (number) deaths per million persons exposed on the basis of epidemiological
risk estimates for ambient particles. These risks are higher than the generally used definition of acceptable risk of 1 × 10−6, but substantially lower than the estimated risks due to ambient particles. Toxicological studies on ambient particles revealed
consistent values for lowest observed effect levels (LOELs) which were converted into equivalent daily uptakes using allometric
scaling. These LOEL uptakes were by a factor of about 330–1,000 (mass) and 1,000–2,500 (particle surface area) higher than
estimated uptakes from printers. This toxicological assessment would indicate no significant health risks due to printer particles.
Finally, our study suggests that particle number (not mass) and mass (not surface area) are the most conservative risk metrics
for the epidemiological and toxicological risks presented here, respectively. 相似文献
15.
D.M. Bubb S.L. Johnson R. Belmont K.E. Schriver R.F. Haglund Jr. C. Antonacci L.-S. Yeung 《Applied Physics A: Materials Science & Processing》2006,83(1):147-151
Low molecular weight polystyrene (∼10 kDa) was ablated with a free-electron laser at 3.31 and 3.43 μm and deposited as thin films on Si(100) substrates. The vibrational bands at 3.31 and 3.43 μm correspond to phenyl-ring CH and backbone CH2 modes, respectively. Even though the absorption coefficients of these two modes are nearly the same, the ablation yield was approximately 50% higher for the ring-mode excitation compared with the backbone mode. Based on spectral line width, the ring-mode lifetime is approximately triple that of the backbone mode, leading to a higher spatiotemporal density of vibrational excitation that more effectively disrupts the relatively weak Van der Waals bonds between neighboring polymer chains and consequently to higher ablation efficiency of the ring mode. Molecular weight assays of the deposited films showed that relatively little bond scission occurred and that the average molecular weight of the films was similar to that of the starting material. PACS 61.41.+e; 78.30.-j; 81.05.Lg; 81.15.Fg 相似文献
16.
We report systematic study of structural, phonon and optical properties of Cr-doped ZnO nanoparticles. These particles are
synthesized through simple sol–gel technique. Structural studies carried out by X-ray diffraction method, confirm that the
prepared particles are in hexagonal wurtzite structure and lattice parameters change considerably while increasing the doping.
Raman and Fourier transform infrared spectral studies show that the intensity of the phonon modes decreased and also blue
shift due to ion doping, respectively. Apart from this, transmission electron microscopic studies show reduction in particle
size where the particle diameters reduced from 36 to 11 nm. Optical absorption spectral measurements show a blue shift in
the band-gap and increment in excitonic oscillator strength. Photoluminescence studies show doping altered the near-band edge
emission but there is no change in the other emission bands which is due to oxygen vacancy, surface defects and surface dangling
bonds. 相似文献
17.
Growth and optical properties of quadrangular zinc oxide nanorods on copper-filled porous silicon 总被引:1,自引:0,他引:1
Zinc oxide (ZnO) nanorods with quadrangular morphology have been successfully prepared on a copper-filled porous silicon substrate using a vapor phase transport method. Scanning electron microscopy showed that the diameters of the nanorods were scattered in a range of 100–400 nm and the lengths up to 2 m. High-resolution transmission electron microscopy and a selected-area electron-diffraction pattern confirmed that the quadrangular ZnO nanorods had a single-crystal wurtzite structure and grew along the (0001) direction. The photoluminescence spectrum under excitation at 325 nm showed an ultraviolet emission at 386 nm and a strong broad green emission at 518 nm at room temperature. PACS 81.05.Dz; 81.05.Rm; 81.07.Bc 相似文献
18.
Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors (Q) and small mode volumes of modes in WGM resonators significantly enhances the light‐matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label‐free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed. 相似文献
19.
Fatemeh Abrishamian Shinichi Nagai Shinya Sato Masaaki Imai 《Optical and Quantum Electronics》2008,40(9):665-676
Spectral response of acoustically induced microbending through thin optical fiber is discussed from mode-coupling of core
and cladding modes. The thin fiber is analyzed in three-layered structure (core-cladding-air) to gain insights into acousto-optic
modulation. We explained the dependence of core and/or cladding diameters on acoustic source parameters from numerical calculations.
According to the calculations, we successfully fabricated all-optical tunable filter using this thin fiber that yields an
efficient mode-coupling at flexural wave frequencies less than 1MHz. To increase the acousto-optic effect, we used a specially
designed thin optical fiber (80 μm of cladding diameter) in the section where flexural wave is produced, and spliced both
ends of the thin fiber to the tapered 125 μm fibers. The frequency and voltage tuning of fabricated filter is also confirmed
by changing the driven frequency and applied voltage of the PZT, respectively. This result suggests a possibility of fiber-optic
device application as all-optical tunable filter at 1.55 μm. 相似文献
20.
Jiaqi Guo Xinwei Wang Lijun Zhang Tao Wang 《Applied Physics A: Materials Science & Processing》2007,89(1):153-156
In this work, the thermal diffusivity of single polyacrylonitrile (PAN) wires with diameters from 4.62 μm down to 324 nm is
measured by using our recently developed transient electro-thermal technique. The wires span from 23 μm to 126.2 μm in our
measurement. Since PAN wires are dielectric, a thin Au film is coated on the surface of the wires to make them conductive.
In the experiment, a step current (with ∼2 μs rising time) is fed to the sample. The sample is heated and takes a certain
time to reach its steady thermal state. The temperature rising response of the sample is sensed by measuring the resistance
change of the thin Au coating. From the average temperature evolution of the sample, the thermal diffusivity can be extracted.
Three PAN wires with different diameters are synthesized using the electro-spinning technique and are measured to obtain their
thermal diffusivities (around 1.53×10-7 m2/s), which are slightly smaller than the bulk value.
PACS 65.80.+n; 66.30.Xj; 44.10.+i 相似文献