共查询到20条相似文献,搜索用时 15 毫秒
1.
We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation
of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic
generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed.
The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together
with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated
with measurements on NO and CO2. The measured isotope ratio 15
NO/14
NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.
Received: 30 April 2002 / Revised version: 10 June 2002 / Published online: 2 September 2002
RID="*"
ID="*"Corresponding author. Fax: +41-1/633-1077, E-mail: sigrist@iqe.phys.ethz.ch 相似文献
2.
M.B. Pushkarsky M.E. Webber O. Baghdassarian L.R. Narasimhan C.K.N. Patel 《Applied physics. B, Lasers and optics》2002,75(2-3):391-396
An industrial trace-ammonia sensor based on photoacoustic spectroscopy and CO2 lasers has been developed for measuring ammonia with a 1σ detection limit of 220 parts-per-trillion (ppt) in an integration
time of 30 s. The instrument response time for measuring ammonia was 200 s, limited by adsorption effects due to the polar
nature of ammonia. The minimum detectable fractional absorbance was 2.0×10-7, and the minimum normalized detectable absorption coefficient for this system was 2.4×10-7 W cm-1/z. The 9R(30) transition of the CO2 laser at 9.22 μm with 2 W of output power was used to probe the strong sR(5,K) multiplet of ammonia at the same wavelength. This sensor was demonstrated with an optically multiplexed configuration
for simultaneous measurement in four cells.
Received: 3 April 2002 / Revised version: 31 May 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-310/458-0171, E-mail: webber@pranalytica.com 相似文献
3.
Development of a tunable mid-IR difference frequency laser source for highly sensitive airborne trace gas detection 总被引:4,自引:0,他引:4
Richter D Fried A Wert BP Walega JG Tittel FK 《Applied physics. B, Lasers and optics》2002,75(2-3):281-288
The development of a compact tunable mid-IR laser system at 3.5 μm for quantitative airborne spectroscopic trace gas absorption
measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled
LiNbO3 and utilizes optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, respectively.
This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well
as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell.
This compact system permits detection of formaldehyde with a minimal detectable concentration (1σ replicate precision) of
74 parts-per-trillion by volume (pptv) for 1 min of averaging time and was achieved using calibrated gas standards, zero air
background and rapid dual-beam subtraction. This corresponds to a pathlength-normalized replicate fractional absorption sensitivity
of 2.5×10-10 cm-1.
Received: 29 April 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-303/497-1492, E-mail: dr@ucar.edu 相似文献
4.
Spectroscopic sensing of gases can be performed with high sensitivity and photometric precision by cavity ringdown (CRD) absorption
spectroscopy. Our cavity ringdown spectrometer incorporates continuous-wave (cw) tunable diode lasers, fibre-optic coupling
and standard photonics and optical telecommunications components. It comprises a rapidly swept optical cavity in a single-ended
optical heterodyne transmitter–receiver configuration, enabling optical absorption of gases to be recorded either as single-frequency
scanned spectra or as simultaneous, multi-wavelength tailored spectra. By measuring weak near-infrared rovibrational spectra
of carbon dioxide gas (CO2), with high resolution in the vicinity of 1.53 μm, we have realised a noise-limited absorption sensitivity of 2.5×10-9 cm-1 Hz-1/2. Analytical sensitivity limits (both actual and projected) and prospective gas-diagnostic applications are discussed. Our
approach to cw-CRD spectroscopy offers high performance in a relatively simple, low-cost, compact instrument that is amenable
to chemical analysis of trace gases in medical, agricultural, industrial and environmental situations.
Received: 16 May 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +61-2/9850-8313, E-mail: brian.orr@mq.edu.au 相似文献
5.
Kosterev AA Curl RF Tittel FK Rochat M Beck M Hofstetter D Faist J 《Applied physics. B, Lasers and optics》2002,75(2-3):351-357
Pulsed thermoelectrically cooled QC-DFB lasers operating at 15.6 μm were characterized for spectroscopic gas sensing applications.
A new method for wavelength scanning based on repetition rate modulation was developed. A non-wavelength-selective pyroelectric
detector was incorporated in the sensor configuration giving the advantage of room-temperature operation and low cost. Absorption
lines of CO2 and H2O were observed in ambient air, providing information about the concentration of these species.
Received: 29 April 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-713/348-5686, E-mail: akoster@rice.edu 相似文献
6.
The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality
is reported. A continuous-wave (cw), external-cavity tunable diode laser centered at 1.55 μm is used to pump an optical cavity
absorption cell in cw-cavity ringdown spectroscopy (cw-CRDS). Preliminary results are presented that demonstrate the sensitivity,
selectivity and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO2, 1.8 ppm for H2O, 19.4 ppb for NH3, 7.9 ppb for HCN and 4.0 ppb for C2H2 are calculated.
Received: 3 April 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-202/994-5873, E-mail: Houston@gwu.edu 相似文献
7.
B. Bakowski L. Corner G. Hancock R. Kotchie R. Peverall G.A.D. Ritchie 《Applied physics. B, Lasers and optics》2002,75(6-7):745-750
Cavity-enhanced absorption spectroscopy is explained in terms of the transmission function of a rapidly swept interferometer,
and the integrated transmission is shown to be proportional to the cavity ringdown time. The technique is demonstrated on
the b1Σg
+-X3Σg
- (1,0) band in molecular oxygen at 687 nm using a tunable diode laser and a relative-ly high-Q optical cavity (finesse ≈4000).
A detection limit of 3×10-8 cm-1 s1/2 is achieved for a 0.8 cm-1 scanning range.
Received: 24 June 2002 / Revised version: 5 August 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: peverall@physchem.ox.ac.uk 相似文献
8.
D.D. Nelson J.H. Shorter J.B. McManus M.S. Zahniser 《Applied physics. B, Lasers and optics》2002,75(2-3):343-350
Non-cryogenic, laser-absorption spectroscopy in the mid-infrared has wide applications for practical detection of trace gases
in the atmosphere. We report measurements of nitric oxide in air with a detection limit less than 1 nmole/mole (<1 ppbv) using
a thermoelectrically cooled quantum cascade laser operated in pulsed mode at 5.26 μm and coupled to a 210-m path length multiple-pass
absorption cell at reduced pressure (50 Torr). The sensitivity of the system is enhanced by operating under pulsing conditions
which reduce the laser line width to 0.010 cm-1 (300 MHz) HWHM, and by normalizing pulse-to-pulse intensity variations with temporal gating on a single HgCdTe detector.
The system is demonstrated by detecting nitric oxide in outside air and comparing results to a conventional tunable diode
laser spectrometer sampling from a common inlet. A detection precision of 0.12 ppb Hz-1/2 is achieved with a liquid-nitrogen-cooled detector. This detection precision corresponds to an absorbance precision of 1×10-5 Hz-1/2 or an absorbance precision per unit path length of 5×10-10 cm-1 Hz-1/2. A precision of 0.3 ppb Hz-1/2 is obtained using a thermoelectrically cooled detector, which allows continuous unattended operation over extended time periods
with a totally cryogen-free instrument.
Received: 1 May 2002 / Revised version: 6 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-978/663-4918, E-mail: ddn@aerodyne.com 相似文献
9.
A pulsed optical parametric oscillator (OPO) operated in an optical cavity with a grazing-incidence grating configuration
(GIOPO) was used for sensitive photoacoustic detection of trace quantities of dinitrogen oxide (N2O). The (ν1+ν3) combination vibration band of N2O was excited with the idler beam of the GIOPO at 2.86 μm using an optical cavity optimized for the idler beam. The linewidth
of the GIOPO could be reduced to 0.4 cm-1, allowing the rotational structure of the absorption spectrum to be resolved. A concentration sensitivity (signal-to-noise
ratio=3) of 60 parts in 109 by volume (60 ppb V) N2O in synthetic air was obtained. This may be sufficient for continuous monitoring of N2O in the atmosphere.
Received: 29 April 2002 / Revised version: 4 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +49-6221/54-4255, E-mail: peter.hess@urz.uni-heidelberg.de 相似文献
10.
G. Totschnig M. Lackner R. Shau M. Ortsiefer J. Rosskopf M.C. Amann F. Winter 《Applied physics. B, Lasers and optics》2003,76(5):603-608
A single-frequency VCSEL has been used for the first time for high-resolution spectroscopy near 1.5 μm. The incorporated buried-tunnel-junction
technology enabled the realization of a long-wavelength InGaAlAs/InP VCSEL with low threshold current (0.925 mA), high output
powers (0.576 mW) and low series resistance (60 Ω). The high-speed tuning capability of the long-wavelength VCSEL was investigated
and used to conduct high-speed absorption spectroscopy. The peak tuning speed was measured to be 3.4 cm-1/μs and a 4.5-cm-1-wide NH3 spectrum was recorded in 2 μs. The VCSEL was used to measure highly resolved low-pressure spectra for pressures ranging from
9.6 mbar to 1 bar. The measured Doppler-broadened linewidth of 0.02 cm-1 agrees within 3% with the theoretical calculations. The availability and various advantages of 1.3–2-μm single-frequency
VCSELs as compared to edge-emitting diode lasers, such as a large current tuning range even at very high tuning frequencies,
and low production costs, should significantly expand the application fields for near-infrared laser gas sensors.
Received: 17 July 2002 / Revised version: 4 December 2002 / Published online: 12 May 2003
RID="*"
ID="*"Corresponding author. Fax: +43-1/58801-15999, E-mail: Gerhard@Totschnig.com 相似文献
11.
F. Kühnemann M. Wolfertz S. Arnold M. Lagemann A. Popp G. Schüler A. Jux W. Boland 《Applied physics. B, Lasers and optics》2002,75(2-3):397-403
A photoacoustic spectrometer for the simultaneous detection of isoprene and the deuterated species [4,4-2H]-2-methyl-1,3-butadiene (isoprene-d2) is presented. Using a sealed-off 13CO2 laser a single-component detection limit of 400 ppt (isoprene) and 600 ppt (isoprene-d2) was achieved. Simultaneous monitoring of both compounds allowed the detection of labelling levels down to 6% (isoprene-d2 in total isoprene) with a time resolution of 3 min.
In emission studies with Eucalyptus globulus, the deuterated precursor [4,4-2H]-1-deoxy-D-xylulose was fed to a leaf through the transpiration stream. Emission of isoprene-d2 started as early as 10 min after application of the precursor.
Received: 3 May 2002 / Revised version: 31 May 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +49-228/733474, E-mail: frank.kuehnemann@iap.uni-bonn.de 相似文献
12.
Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy 总被引:3,自引:0,他引:3
A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements
of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis
trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant
unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of
approximately 3.1×10-11 cm-1 Hz-1/2. The instrument has been used for sensitive measurements of CO, CH4, C2H2 and NH3.
Received: 6 May 2002 / Revised version: 31 May 2002 / Published online: 2 September 2002
RID="*"
ID="*"Corresponding author. Fax: +1-650/965-7074, E-mail: d.baer@lgrinc.com 相似文献
13.
V.L. Kasyutich C.E. Canosa-Mas C. Pfrang S. Vaughan R.P. Wayne 《Applied physics. B, Lasers and optics》2002,75(6-7):755-761
We present an application of continuous-wave (cw) cavity-enhanced absorption spectroscopy (CEAS) with off-axis alignment geometry
of the cavity and with time integration of the cavity output intensity for detection of narrow-band and broadband absorbers
using single-mode red diode lasers at λ=687.1 nm and λ=662 nm, respectively. Off-axis cw CEAS was applied to kinetic studies
of the nitrate radical using a broadband absorption line at λ=662 nm. A rate constant for the reaction between the nitrate
radical and E-but-2-eneof (3.78±0.17)×10-13 cm3 molecule-1 s-1 was measured using a discharge-flow system. A nitrate-radical noise-equivalent (1σ≡ root-mean-square variation of the signal)
detection sensitivity of 5.5×109 molecule cm-3 was achieved in a flow tube with a diameter of 4 cm and for a mirror reflectivity of ∼99.9% and a lock-in amplifier time
constant of 3 s. In this case, a noise-equivalent fractional absorption per one optical pass of 1.6×10-6 was demonstrated at a detection bandwidth of 1 Hz. A wavelength-modulation technique (modulation frequency of 10 kHz) in
conjunction with off-axis cw CEAS has also been used for recording 1f- and 2f-harmonic spectra of the RR(15) absorption of the b1Σg
+-X3Σg
- (1,0) band of molecular oxygen at =14553.947 cm-1. Noise-equivalent fractional absorptions per one optical pass of 1.35×10-5, 6.9×10-7 and 1.9×10-6 were obtained for direct detection of the time-integrated cavity output intensity, 1f- and 2f-harmonic detection, respectively,
with a mirror reflectivity of ∼99.8%, a cavity length of 0.22 m and a detection bandwidth of 1 Hz.
Received: 24 June 2002 / Revised version: 12 August 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: vlk@physchem.ox.ac.uk 相似文献
14.
The use of mid-infrared polarization spectroscopy (PS) for the detection of CO2 has been demonstrated. The P(13) and P(14) resonances of the (0 00 0)→(1 00 1) transition of CO2 were probed using a single-mode optical parametric generator system to produce a high-intensity laser beam at approximately
2.7 μm. The experiments were performed in an atmospheric pressure CO2 jet and also in a sub-atmospheric pressure gas cell. The experimental results were compared with the results of the time-dependent
density-matrix equations using direct numerical integration. The Zeeman-state structure of the upper and lower energy levels
was included in the multi-state formulation of the density-matrix equations. Fifty-eight Zeeman states and two bath levels
were included in the numerical analysis of the P(14) transition. The measured and calculated PS line shapes were in good agreement,
and the absolute experimental signal level agreed with the theoretical calculation to within a factor of five.
Received: 20 March 2002 / Revised version: 16 August 2002 / Published online: 11 December 2002
RID="*"
ID="*"Present address: Innovative Scientific Solutions Inc., 2766 Indian Ripple Road, Dayton, OH 45 440, USA
RID="**"
ID="**"Corresponding author. Fax: +1-765/494-0539, E-mail: Lucht@purdue.edu
RID="***"
ID="***"Present address: School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47807-2040 USA 相似文献
15.
E. Schlosser J. Wolfrum L. Hildebrandt H. Seifert B. Oser V. Ebert 《Applied physics. B, Lasers and optics》2002,75(2-3):237-247
The residence-time of the flue gas in a furnace is an important parameter for a complete and clean combustion. A new method
to determine the residence-time has been developed and is presented for the first time. It is based on the injection of alkali
compounds as a tracer. Alkali atoms that are produced by thermal decomposition of the tracer are detected in the hot flue
gas after passage of the combustion facility. This is done without any gas sampling using direct tunable diode laser based
absorption spectroscopy. Different diode laser (DL) types (Fabry–Pérot DLs, external-cavity DLs, and vertical-cavity surface-emitting
lasers) were analyzed and used to develop several spectrometers for the in situ detection of lithium (671 nm), potassium (770 nm), and rubidium (780 nm). Various spectrometers were built for single- or
multi-species detection using a single laser, for time-multiplexed multi-species detection using two lasers, and for multi-path
detection at two different locations along the flue-gas duct. To evaluate the system performance the potassium atom background
caused by the fuel was continuously monitored in the post-combustion chamber (PCC) for several weeks. A typical concentration
range of 1 ng to 1 μg at STP (800 ppq to 800 ppt; ppq=10-15) was observed. By averaging 100 individual absorption scans the response time was 2.7 s. The minimum detectable absorption
was about 10-4 optical density, corresponding to a detection limit of 4×1011 K atoms/m3 at 1200 K instead of ‘°K’. (K(D2) absorption line; 1.9-m absorption path). This is equivalent to a detection limit of 0.1 ng/m3 at STP or 80 ppq. The fastest response time (0.16 s) was achieved by evaluating single absorption scans. Two combustion facilities
at the Forschungszentrum Karlsruhe (a batch combustor and a 3-MW special waste incinerator with a rotary kiln followed by
a PCC) were investigated. Alkali chlorides were added to the combustion chamber in different forms, of which short spray pulses
of an aqueous salt solution was the method of choice for the residence-time measurement. Flow-time distributions were measured
and the mean residence-time was calculated for various operation conditions. A simultaneous flow-time measurement at two different
locations (8.4 m/17.0 m from the tracer discharge location) was realized with a binary K/Rb tracer and a multi-species spectrometer.
Mean residence-times of (±) 151s and (±) 261s were observed and met the expected values.
Received: 29 April 2002 / Revised version: 21 June 2002 / Published online: 2 September 2002
RID="*"
ID="*"Corresponding author. Fax: +49-6221/5450-50, E-mail: volker.ebert@pci.uni-heidelberg.de
This paper is dedicated to Prof. Dr. Gottfried Huttner on the occasion of his 65th birthday. 相似文献
16.
S.T. Sanders 《Applied physics. B, Lasers and optics》2002,75(6-7):799-802
A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear
fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm)
pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive
fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety
of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately
1 cm-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad,
rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H2O, CO2, C2H2 and C2H6O at a pressure of 10 bar.
Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu 相似文献
17.
By optically pumping the deuterated isotopomers of 14NH3 and 15NH3 using 12C16O2, 13C16O2, 12C18O2, and 13C18O2 lasers, several new far-infrared (FIR) emission lines between 65 μm and 125 μm have been detected. The existing spectroscopy
of 14N-ammonia isotopomers has been used to identify many of these lines, as well as some previously observed but unidentified.
The spectroscopic data have been analyzed to predict over 20 additional FIR laser lines that could be pumped by a more capable
CO2 laser. This effort was motivated by a need for strong laser lines in frequency coincidence with molecular transitions of
astrophysical interest. Of particularnote is the measurement of the 2680-GHz line of 14NHD2, whose frequency is 4.9 GHz higher than that of the important J=1-0 line of interstellar HD.
Received: 25 July 2002 / Published online: 20 December 2002
RID="*"
ID="*"Corresponding author. Fax: +1-303/492-5941, E-mail: boreiko@spot.colorado.edu 相似文献
18.
Rapid formaldehyde monitoring in ambient air by means of mid-infrared cavity leak-out spectroscopy 总被引:1,自引:0,他引:1
H. Dahnke G. von Basum K. Kleinermanns P. Hering M. Mürtz 《Applied physics. B, Lasers and optics》2002,75(2-3):311-316
We report the spectroscopic detection of formaldehyde in ambient air using cavity leak-out spectroscopy, a cw variant of cavity
ring-down spectroscopy. This technique proved to be suitable for a real-time quantitative analysis of polluted air without
any preprocessing of the air sample. Using a tunable CO-overtone sideband laser for the λ=3 μm spectral region and a ring-down
cell with R=99.95% mirrors, we achieved a detection limit of 2 parts per billion formaldehyde in ambient air, corresponding
to a minimum detectable absorption coefficient of 7×10-9/cm (sampling time: 2 s). Calibration problems arising from the polarity of the molecule and due to HITRAN database uncertainties
are discussed.
Received: 28 March 2002 / Revised version: 7 June 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +49-211/811-3121, E-mail: muertz@uni-duesseldorf.de 相似文献
19.
A. Castrillo G. Casa E. Kerstel L. Gianfrani 《Applied physics. B, Lasers and optics》2005,81(6):863-869
Near-infrared laser spectroscopy is used to measure the 13C/12C isotope abundance ratio in gas phase carbon dioxide. The spectrometer, developed expressly for field applications, is based
on a 2 μm distributed feedback diode laser in combination with sensitive wavelength modulation detection. It is characterized
by a simplified optical layout, in which a single detector and associated electronics are used to probe absorptions of a pair
of 13CO2 and 12CO2 lines, simultaneously in a sample, as well as a reference gas. For a careful investigation of the achievable precision and
accuracy levels, we carried out a variety of laboratory tests on CO2 samples with different isotopic compositions, calibrated with respect to the international standard material by means of
isotope ratio mass spectrometry. The 1-σ accuracy of the 13CO2/12CO2 determinations, reported in the so-called δ notation, is about 0.5‰ (including both statistical and systematic errors), for
δ-values in the range from -30‰ to +20‰. We show that the major source of systematic errors is a consequence of the non-linearity
of the Lambert–Beer absorption law, and can be corrected for to a very high degree of accuracy.
PACS 42.62.Fi; 42.55.Px; 33.20.Ea 相似文献
20.
Results are given for thermal tuning and modulation of a 1556-nm distributed feedback fibre laser by resistive heating of
a thin silver film chemically deposited on the fibre. Without reaching the limits of performance, linear tuning is demonstrated
at a rate of 1.72 pm/mW up to about 200 pm, and a peak-to-peak modulation of 100 MHz up to modulation frequencies of 60 Hz.
The heat flow is analyzed, and the coated fibre is characterized in terms of the static and dynamic wavelength response to
the applied electric power. The performance of the scheme is tested by recording part of the ν1+ν3 combination band spectrum of 13C2H2 with thermal modulation and scanning of the fibre laser.
Received: 12 March 2002 / Revised version: 24 June 2002 / Published online: 25 September 2002
RID="*"
ID="*"Corresponding author. Fax: +45/4593-1137, E-mail: sus@dfm.dtu.dk 相似文献