共查询到20条相似文献,搜索用时 31 毫秒
1.
Objective:
The objective in this work is to investigate the feasibility of using a new imaging tool called vibro-acoustography (VA) as a means of permanent prostate brachytherapy (PPB) seed localization to facilitate post-implant dosimetry (PID).Methods and materials:
Twelve OncoSeed (standard) and eleven EchoSeed (echogenic) dummy seeds were implanted in a human cadaver prostate. Seventeen seeds remained after radical retropubic prostatectomy. VA imaging was conducted on the prostate that was cast in a gel phantom and placed in a tank of degassed water. 2-D magnitude and phase VA image slices were obtained at different depths within the prostate showing location and orientation of the seeds.Results:
VA demonstrates that twelve of seventeen (71%) seeds implanted were visible in the VA image, and the remainder were obscured by intra-prostatic calcifications. Moreover, it is shown here that VA is capable of imaging and locating PPB seeds within the prostate independent of seed orientation, and the resulting images are speckle free.Conclusion:
The results presented in this research show that VA allows seed detection within a human prostate regardless of their orientation, as well as imaging intra-prostatic calcifications. 相似文献2.
Using group theory calculations combined with the force-constant model and molecular-dynamics simulations, whether the deformed modes are Raman active or not for (10,10) and (10,0) single-wall carbon nanotubes under hydrostatic pressure is discussed. With increasing pressure, the tube symmetry lowers from D20h to D2h then to C2h point group. For D20h, A1g is changed to Ag, while E1g and E2g are split: E1g→B2g+B3g→2Bg and E2g→Ag+B1g→2Ag. On the basis of the correlation between D20h, D2h, and C2h point groups, the deformed modes should be still Raman active. The result can help us clarify the essence of the experimental observations. 相似文献
3.
Alessandra Fonseca Lucrédio 《Applied Surface Science》2009,255(11):5851-5856
Catalysts’ precursor of Co/Mg/Al promoted with Ce and La were tested in the steam reforming of methane (SRM). The addition of promoters was made by anion-exchange. The oxides characterization was made by X-ray Photoelectron Spectroscopy (XPS) analysis that confirmed Co2+ species in free form on surface and interacted with Mg and Al in the form of solid solution. In the SRM with high fed molar ratio of H2O:CH4 = 4:1, the catalysts showed a great affinity with water and immediately deactivated by oxidation of the active sites. In the stoichiometric ratio of H2O:CH4 = 2:1 the catalysts were active and presented low carbon deposition during the time reaction tested. Also a test with low fed molar ratio H2O:CH4 = 0.5:1 was carried out to evaluate the stability of the catalysts by CH4 decomposition and all the catalysts were stable during 6 h of reaction. Promoted catalysts presented lower carbon deposition. 相似文献
4.
Work function of single-walled carbon nanotubes determined by field emission microscopy 总被引:2,自引:0,他引:2
J.P. Sun Z.X. Zhang S.M. Hou G.M. Zhang Z.N. Gu X.Y. Zhao W.M. Liu Z.Q. Xue 《Applied Physics A: Materials Science & Processing》2002,75(4):479-483
The field emission characteristics of a single micro-bundle of single-walled carbon nanotubes (SWCNTs) were investigated using
field emission microscopy (FEM). Fowler–Nordheim plots revealed that the work function of the SWCNTs was reduced with increasing
heating temperature, and reached a minimum value around 1000 °C, assuming that the β factor was constant during the heating
process. Field emission patterns also demonstrated fine structures that were believed to be images of the cap of a SWCNT,
which was in a clean state. The radius of the SWCNT micro-bundle was measured by transmission electron microscopy (TEM), and
the β factor was calculated using two empirical formulae. Then, the work function of the SWCNT was determined from the slope,
K, of its Fowler–Nordheim plot. The work function values were Φ1=4.76 eV and Φ2=4.88 eV, respectively.
Received: 26 October 2001 / Revised version: 19 February 2002 / Published online: 6 June 2002 相似文献
5.
The subject of our studies was determination of the kind and strength of the catalyst acid centres on isopropyl alcohol conversion. The investigations were carried out for two groups of catalysts: typical Lewis acids γ-Al2O3 and ZrO2 and Brønsted acids: H3PW12O40 and H3PMo12O40. Considerable differences between Lewis and Brønsted acids in the conversion of isopropyl alcohol were observed. The influence of Brønsted acid centres was studied for a group of catalysts with different strength: mixtures of two different heteropolyacids. It was observed that the increasing strength of Brønsted acids centres leads to higher catalytic activity but it does not significantly affect the activation energy of dehydration to propene. 相似文献
6.
J. Hone M.C. Llaguno M.J. Biercuk A.T. Johnson B. Batlogg Z. Benes J.E. Fischer 《Applied Physics A: Materials Science & Processing》2002,74(3):339-343
The thermal properties of carbon nanotubes are directly related to their unique structure and small size. Because of these
properties, nanotubes may prove to be an ideal material for the study of low-dimensional phonon physics, and for thermal management,
both on the macro- and the micro-scale. We have begun to explore the thermal properties of nanotubes by measuring the specific
heat and thermal conductivity of bulk SWNT samples. In addition, we have synthesized nanotube-based composite materials and
measured their thermal conductivity.
The measured specific heat of single-walled nanotubes differs from that of both 2D graphene and 3D graphite, especially at
low temperatures, where 1D quantization of the phonon bandstructure is observed. The measured specific heat shows only weak
effects of intertube coupling in nanotube bundling, suggesting that this coupling is weaker than expected. The thermal conductivity
of nanotubes is large, even in bulk samples: aligned bundles of SWNTs show a thermal conductivity of >200 W/m K at room temperature.
A linear K(T) up to approximately 40 K may be due to 1D quantization; measurement of K(T) of samples with different average
nanotube diameters supports this interpretation.
Nanotube–epoxy blends show significantly enhanced thermal conductivity, showing that nanotube-based composites may be useful
not only for their potentially high strength, but also for their potentially high thermal conductivity.
Received: 17 October 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002 相似文献
7.
D.N. Kozlov B. Hemmerling A. Stampanoni-Panariello 《Applied physics. B, Lasers and optics》2000,71(4):585-591
We used time-resolved light scattering of cw probe laser radiation from laser-induced electrostrictive gratings for the determination
of flow velocities in air at room temperature. Some possibilities of the technique have been experimentally demonstrated with
submerged planar air jets in atmosphere, both for accumulated and single-shot measurements. The range of investigated flow
velocities was 5–200 m/s. The method of data treatment and of the estimate of the experimental parameters is described.
Received: 8 Febuary 2000 / Revised version: 2 May 2000 / Published online: 2 August 2000 相似文献
8.
We report here an experimental observation of field emission from arrays of multiwall carbon nanotubes. Current densities
in the range 10–30 mA/cm2 with excellent long-term stability were recorded. A detailed study of the destruction of nanotubes at extreme operation conditions
is performed. We established that field evaporation of nanotubes accompanies field emission from a cold cathode at electric
fields higher than 2 V/?. Electron microscopy of the evaporation products reveals irregularly shaped carbon nanoparticles
with a hollow core. The diameter of the particles is ∼20 nm. A mechanism of the process is proposed and discussed.
Received: 6 October 2000 / Accepted: 28 April 2001 / Published online: 27 June 2001 相似文献
9.
Zhenfa Zi Yuping Sun Xuebin Zhu Jianming Dai 《Journal of magnetism and magnetic materials》2009,321(9):1251-1255
CoFe2O4 ferrite nanoparticles were prepared by a modified chemical coprecipitation route. Structural and magnetic properties were systematically investigated. X-ray diffraction results showed that the sample was in single phase with the space group . The results of field-emission scanning electronic microscopy showed that the grains appeared spherical with diameters ranging from 20 to 30 nm. The composition determined by energy-dispersive spectroscopy was stoichiometry of CoFe2O4. The Curie temperature in the process of increasing temperature was slightly higher than that in the process of decreasing temperature. This can be understood by the fact that heating changed Co2+ ion redistribution in tetrahedral and in octahedral sites. The coercivity of the synthesized CoFe2O4 samples was lower than the theoretical values, which could be explained by the mono-domain structure and a transformation from ferrimagnetic to superparamagnetic state. 相似文献
10.
The formation and thermostability of MgO and MgAl2O4 nanoparticles in oxidized SiC particle-reinforced Al-Mg composites 总被引:2,自引:0,他引:2
Z. Shi S. Ochiai M. Gu M. Hojo J.C. Lee 《Applied Physics A: Materials Science & Processing》2002,74(1):97-104
Interfacial reactions and their products in oxidized SiC particle-reinforced Al-Mg matrix composites were investigated using
X-ray diffraction and Field EmissionScanning Electron Microscopy (FE-SEM). Observation of the interfacial reaction between
oxidized SiC particles and aluminum alloys containing Mg showed that nanoparticles of MgO form initially and do not change
form when more than 4 wt. % Mg is in the matrix. However, MgO transforms into octahedral MgAl2O4 crystals when less than 2 wt. % Mg is in the matrix .Comparison of the amounts and the sizes of the reaction products MgAl2O4 and MgO between the Al-Mg alloyswith different matrix compositions shows that fewer MgAl2O4 crystals form at the surface of the particles in the 2014Al matrix composite than in the Al-2 wt. % Mg (Al-2Mg) matrix composite.
Also, the size of MgAl2O4 in the former composite is greater than that of the latter composite under the same conditions. However, the amount and the
size of MgO crystals that form in the Al-4 wt. % Mg (Al-4Mg) matrix composite is almost the same as that of the Al-8 wt. %
Mg (Al-8Mg) composite, and the size of MgO changes a little during heat-treatment at elevated temperatures. The amount of
the reaction product (either MgO or MgAl2O4) depends on nucleation rates and density of nucleation sites on the oxidized SiC particles at the initial reaction. The more
completely the nuclei cover the surface of the oxidized SiC particles, the smaller the resulting size. According to the results,
an addition of Mg into the matrix can be used to control the interfacial characteristics in the oxidized SiC/Al composites.
Received: 25 January 2001 / Accepted: 26 January 2001 / Published online: 23 May 2001 相似文献
11.
D. Golberg P.S. Dorozhkin Y. Bando Z.-C. Dong C.C. Tang Y. Uemura N. Grobert M. Reyes-Reyes H. Terrones M. Terrones 《Applied Physics A: Materials Science & Processing》2003,76(4):499-507
Transport and field-emission properties of as-synthesized CNx and BNCx (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those
were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron
microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas
those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission
properties with emitting currents per rope reaching ∼4 μA(CNx) and ∼2 μA (BNCx), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm2 (BNCx) and 5.5 mA/cm2 (CNx) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing
the current density to 0.2–0.4 A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.
Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp 相似文献
12.
In this work, we have studied the sorption of selenium (79Se is one of the main radionuclides in a spent nuclear fuel repository) on magnetite (Fe3O4), a mineral present in the near-field of a nuclear waste repository that might represent an important retardation factor for the mobility of many radionuclides.The sorption of both Se(IV) and Se(VI) onto magnetite has been fitted by a non-competitive Langmuir isotherm with Γmax = (3.13 ± 0.07) × 10−6 mol m−2 and KL = (1.19 ± 0.07) × 106 dm3 mol−1 for Se(IV) and Γmax = (3.5 ± 0.2) × 10−6 mol m−2 and KL = (3.0 ± 0.1) × 105 dm3 mol−1 for Se(VI).The variation of the sorption of selenium with pH has been modeled using the Triple Layer Surface Complexation Model and the equilibrium constants between selenium and magnetite have been obtained using the FITEQL program. For the case of Se(IV), the best fitting has been obtained using two inner-sphere complexes, FeOHSeO32− and FeHSeO3, while for Se(VI), the best fitting has been obtained considering only an outer-sphere complex, FeOH2+SeO42−.The surface complexation reactions derived in this work are in agreement with those stated by other authors for sorption of Se(IV) and Se(VI) on hydrous iron oxides. 相似文献
13.
F.G. Wienhold H. Fischer P. Hoor V. Wagner R. Königstedt G.W. Harris J. Anders R. Grisar M. Knothe W.J. Riedel F.-J. Lübken T. Schilling 《Applied physics. B, Lasers and optics》1998,67(4):411-417
2 O during two airborne polar stratospheric campaigns in January and March 1997. These species were detected using integration
periods of 1 s with a precision of ±2%(3σ) and a calibration accuracy of ±2.8% during a total of 11 measurement flights up
to a maximum altitude of 12.5 km. More recently all three channels have been operated simultaneously for CO, CH4, and N2O with comparable results.
Received: 5 March 1998 相似文献
14.
Coupled thermal and carrier transports (electron/hole generation, recombination, diffusion and drifting) in laser photoetching
of GaAs thin film is investigated. A new volumetric heating mechanism originating from SRH (Shockley–Read–Hall) non-radiative
recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating
and Joule heating are found to be important in the carrier transport, as well as the etching process. SRH heating and Joule
heating are primarily confined within the space-charge region, which is about 20 nm from the GaAs surface. The surface temperature
rises rapidly as the laser intensity exceeds 105 W/m2. Below a laser intensity of 105 W/m2, the thermal effect is negligible. The etch rate is found to be dependent on the competition between photovoltaic and photothermal
effects on surface potential. At high laser intensity, the etch rate is increased by more than 100%, due to SRH and Joule
heating.
Received: 24 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. Fax: +1-310/206-2302, E-mail: xiang@seas.ucla.edu 相似文献
15.
The iron(III)-ion doped TiO2 (Fe3+-TiO2) with different doping Fe3+ content were prepared via a sol-gel method. The as-prepared Fe3+-TiO2 nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe3+-TiO2 catalysts with different Fe3+ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe3+-TiO2 was revealed: that is, the Fe3+ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti ≤ 0.03 mol%); while Fe3+ dopant content exceeds 0.03 mol%, Fe2O3 became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe2O3 with TiO2 leads to that the photoinduced electrons and holes of TiO2 transfer to Fe2O3 and recombine quickly, which is unfavorable to the photocatalytic reaction. 相似文献
16.
The dynamic acoustic radiation force resulting from a dual-frequency beam incident on spherical shells immersed in an inviscid fluid is examined theoretically in relation to their thickness and the contents of their interior hollow regions. The theory is modified to include a hysteresis type of absorption inside the shells' material. The results of numerical calculations are presented for stainless steel and absorbing lucite (PolyMethyMethacrylAte) shells with the hollow region filled with water or air. Significant differences occur when the interior fluid inside the hollow region is changed from water to air. It is shown that the dynamic radiation force function Yd deviates from the static radiation force function Yp when the modulation size parameter deltax = mid R:x2 - x1mid R: (x1 = k1a, x2 = k2a, k1 and k2 are the wave vectors of the incident ultrasound waves, and a is the outer radius of the shell) starts to exceed the width of the resonance peaks in the Yp curves. 相似文献
17.
2 laser photoacoustic spectrometer has been developed for the in-situ monitoring of atmospheric trace gases in different environments.
Numerous air pollutants, such as ammonia, ethene, ozone and alcohols, can be monitored with a time resolution of a few minutes.
A new fitting algorithm based on the numerical method of Levenberg–Marquardt is discussed and applied to the derivation of
individual gas concentrations from measured photoacoustic signal amplitudes and phases at selected CO2 laser wavelengths. The algorithm has been tested with artificially generated multicomponent gas mixtures exhibiting gas concentrations
in the ppb to ppm range. Furthermore, its potential is demonstrated with the analysis of an air sample from a fruit storage
chamber and with ambient air measurements during a field study in a rural environment.
Received: 23 March 1998/Revised version: 18 June 1998 相似文献
18.
High-quality GaN nanowires synthesized using a CVD approach 总被引:3,自引:0,他引:3
High-quality GaN nanowires were synthesized on a large-area Si substrate by direct reaction of gallium with ammonia using
InCl3 as a catalyst. The morphology and microstructure of the resulting products were characterized using a field-emission scanning
electron microscope (SEM), a high-resolution transmission electron microscope, and X-ray diffraction (XRD). XRD and electron
diffraction revealed that the nanowires are of a hexagonal GaN phase with the wurtzite structure. The SEM study showed that
the nanowires are straight and have a smooth morphology with lengths up to 500 μm. The present results reveal that InCl3 is an optimal catalyst in GaN nanowire production.
Received: 2 April 2002 / Accepted: 12 April 2002 / Published online: 19 July 2002 相似文献
19.
Gul Gulpinar 《Physics letters. A》2008,372(2):98-105
In this study, the sound attenuation coefficient of a spin- metamagnetic Ising system is calculated by the method of thermodynamics of irreversible processes. The behavior of sound attenuation near the phase transition temperatures is analyzed according to various values of phenomenological rate coefficients (γij). For all γm and γs values it is found that sound attenuation peaks occur below TN(H) and depend on frequency ω and the value of the off-diagonal rate coefficient γ. On the other hand, the critical behavior of the sound attenuation in the hydrodynamic regime is obtained analytically via the critical exponents. Moreover, the behavior of the sound attenuation as a function of frequency is also investigated and ω2 dependence is observed for the attenuation coefficient. These results are in a good agreement with ultrasonic investigations of magnetic systems. 相似文献
20.
K.H. Heinig T. Müller B. Schmidt M. Strobel W. Möller 《Applied Physics A: Materials Science & Processing》2003,77(1):17-25
We have investigated the synthesis of nanostructures, as well as the control of their size and location by means of ion beams.
The phase separation and interface kinetics under ion irradiation give new possibilities for controlling the growth of nanostructures.
Additionally, the chemical decomposition of the host matrix by collisional mixing can contribute to the self-organization
of nanostructures, especially at interfaces. It is shown how collisional mixing during ion implantation affects nanocrystal
(NC) synthesis and how ion irradiation through NCs modifies their size and size distribution. An analytical expression for
solute concentration around an ion-irradiated NC was found, which may be written like the well-known Gibbs–Thomson relation.
However, parameters have modified meanings, which has a significant impact on the evolution of NC ensembles. “Inverse Ostwald
ripening” of NCs, resulting in an unimodal NC size distribution, is predicted, which has been confirmed experimentally for
Au NCs in SiO2 and by kinetic lattice Monte Carlo simulations. At interfaces, the same ion-irradiation-induced mechanism may result in self-organization
of NCs into a thin δ-layer. Collisional decomposition of SiO2 may enhance the NC δ-layer formation in SiO2 at the Si/SiO2 interface. The distance of the self-organized NC δ-layer from the SiO2/Si interface renders the structure interesting for non-volatile memory applications.
Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003
RID="*"
ID="*"Corresponding author. Fax: +49-351-260-3285, E-mail: K.-H.Heinig@fz-rossendorf.de 相似文献