共查询到20条相似文献,搜索用时 46 毫秒
1.
A simple, accurate and reliable method for measuring the reflectivity of lasergrade mirrors (R > 99.5%) based on cavity ring-down (CRD) technique has been successfully demonstrated in our laboratory using a pulsed Nd:YAG
laser. A fast photomultiplier tube with an oscilloscope was used to detect and analyse the CRD signal. The cavity decay times
were measured for three cavities formed by a combination of three mirror pairs. The absolute reflectivities R
1, R
2, R
3 were determined to be 99.94%, 99.63%, 99.52% at normal incidence. The reflectivity of mirrors is measured to an accuracy
of 0.01%. 相似文献
2.
The absolute, quantitative spatially resolved distribution of CH radicals was measured in the reaction zone of a low-pressure methane/air flame (25 Torr) using a combination of laser-induced fluorescence (LIF) and cavity ring-down (CRD) absorption spectroscopy operating on the A2–X2(0,0) transition. The spatially resolved 1-D image of LIF provides a direct measure of the CH distribution along the path of the laser beam in the CRD cavity. The temperature distribution was determined from measurements on a pair of rotational transitions. A series of LIF line images and CRD absorption measurements taken at various burner heights are combined to form a quantitative 2-D image of the CH distribution. This is used to interpret the CRD measurements along this inhomogeneous path. The 10 ppm peak CH concentration measured here on the centerline of the flame is in good agreement (within 15%) with earlier CH A–X LIF measurements calibrated by Rayleigh and Raman scattering. A 1-D LIF image collected simultaneously with CRD absorption was also used to quantify and optimize the spatial resolution of the CRD measurement. PACS 42.62.Fi; 82.33.Vx; 33.80.Gj 相似文献
3.
A.A. Ruth T. FernholzR.P. Brint M.W.D. Mansfield 《Journal of Molecular Spectroscopy》2002,214(1):80-86
The T1←S0 absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550-620 nm) and in a seeded cold supersonic jet (580-600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of ∼±5%. In this region 22 harmonic sequences and 18 hot bands were observed. The energetically lowest ground state vibration at 167.5 cm−1 was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm−1. The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S1, 0←S0, 0 absorption was tentatively assigned to a transition at ∼17433 cm−1. 相似文献
4.
J. Luque J.B. Jeffries G.P. Smith D.R. Crosley 《Applied physics. B, Lasers and optics》2001,73(7):731-738
The combination of two-dimensional, planar laser-induced fluorescence (PLIF) and cavity ring-down (CRD) absorption spectroscopy
is applied to map quantitatively the spatial distributions of CH2O and CH in a methane/air flame at 25 Torr. Both species are detected in the same spectral region using the overlapping CH2O A 1
A
2
-X
1
A
1
41
0 and CH B-X(1,0 )bands. The combination of diagnostic techniques exploits the spatial resolution of LIF and the quantitative
CRD absorption measure of column density. The spatially resolved PLIF provides the distribution of absorbers and line-of-sight
CRD absorption the absolute number density needed for quantitative concentration images. The peak CH2O concentration is (3.5±1.4 )×1014 cm-3, or 1450±550 ppm at 1000 K. The lack of precise absorption cross-section data produces these large error limits. Although
a flame model predicts lower amounts, these large uncertainties limit this measurement’susefulness as a test of the flame
chemistry.
Received: 24 April 2001 / Revised version: 10 July 2001 / Published online: 10 October 2001 相似文献
5.
BackgroundCardiac magnetic resonance imaging (MRI) is emerging as an important imaging tool in the assessment of heart failure with preserved ejection fraction (HFpEF). This systematic review and meta-analysis aim to synthesise and consolidate the current literature on cardiac MRI for prognostication of HFpEF.Methods designSystematic review and meta-analysis. Data sources: Scopus (PubMed and Embase) for studies published between 2008 and 2019. Eligibility criteria for study selection were studies that evaluated the prognostic role of cardiac MRI in HFpEF. Random effects meta-analyses of the reported hazard ratios (HR) for clinical outcomes was performed.ResultsInitial screening identified 97 studies. From these, only nine (9%) studies met all the criteria. The main cardiac MRI methods that demonstrated association to prognosis in HFpEF included late gadolinium enhancement (LGE) assessment of scar (n = 3), tissue characterisation with T1-mapping (n = 4), myocardial ischaemia (n = 1) and right ventricular dysfunction (RVSD) (n = 1). The pooled HR for all 9 studies was 1.52 (95% CI 1.05–1.99, P < 0.01). Sub-evaluation by cardiac MRI methods revealed varying HRs: LGE (net n = 402, HR = 1.6, 95% CI 0.42–2.78, P = 0.008); T1-mapping (n = 1623, HR = 1.25, 95% CI 0.891–1.60, P < 0.001); myocardial ischaemia or RVSD (n = 325, HR = 3.19, 95% CI 0.30–6.08, P = 0.03).ConclusionThis meta-analysis demonstrates that multiparametric cardiac MRI has value in prognostication of patients with HFpEF. HFpEF patients with a detectable scar on LGE, fibrosis on T1-mapping, myocardial ischaemia or RVSD appear to have a worse prognosis.PROSPERO registration numberCRD42020187228. 相似文献
6.
M. Mazurenka R. Wada A. J. L. Shillings T. J. A. Butler J. M. Beames A. J. Orr-Ewing 《Applied physics. B, Lasers and optics》2005,81(1):135-141
A fast Fourier transform (FFT) method for analysis of ring-down decays from a cavity ring-down (CRD) spectrometer has been tested and compared with alternative fitting methods. The ring-down times derived from the FFT method are obtained with a precision close to that of the Levenberg–Marquardt non-linear least-squares method, but the fitting algorithm is ~100 times faster, allowing real-time fitting of individual ring-down traces on a personal computer. Advantages of the FFT method are discussed, and the method is demonstrated for the measurement of NO2 partial pressures equivalent to mixing ratios of 150 pptv and above in laboratory air, using a CRD spectrometer based on an external cavity diode laser operating at wavelengths around 410 nm. The absorption by NO2 is distinguished from other cavity losses either by using synthetic (zero) air reference samples, or by diverting the sampled laboratory airflow through an NO2 chemical scrubber consisting of hydroxyapatite on a TiO2 substrate. Typical mixing ratios of NO2 in the laboratory air are ~25 ppbv. 相似文献
7.
Katharina Salffner Michael Böhm Oliver Reich Hans-Gerd Löhmannsröben 《Applied physics. B, Lasers and optics》2014,116(4):785-792
We report on the development of a cavity ring-down (CRD) spectrometer based on an incoherent broadband light source centered at 1,545 nm. One measurement spans over 46 nm. Due to the challenge of broadband CRD spectroscopy in the addressed spectral range, an extended measurement principle is developed. First successful measurements in the spectral range between 1,547 and 1,593 nm of a cavity filled with CO2 are shown. In order to compare the experimentally determined data to values of the HITRAN database, the calculation of the expected values is discussed under consideration of the spectrometer’s spectral resolution. Comparison with the data based on the HITRAN database shows good agreement. 相似文献
8.
Hongjiang Ren 《Molecular physics》2013,111(23):3663-3672
The mechanism of H abstraction reactions for Isoflurane with the OH radical was investigated using density functional theory and G3(MP2) duel theory methods. The geometrical structures of all the species were fully optimised at B3LYP/6-311++G** level of theory. Thermochemistry data were obtained by utilising the high accurate model chemistry method G3(MP2) combined with the standard statistical thermodynamic calculations. Gibbs free energies were used for the reaction channels analysis. All the reaction channels were confirmed throughout the intrinsic reaction coordinate analysis. The results show that two channels were obtained, which correspond to P(1) and P(2) with the respective activation barriers of 63.03 and 54.82 kJ/mol. The rate constants for the two channels over a wide temperature range of 298.15–2000 K were predicted and the calculated data are in agreement with the experimental one. The results show that P(2) is the dominant reaction channel under 800 K and above 800 K, it can be found that P(1) will be more preferable reaction channel. 相似文献
9.
K. Bescherer J. A. Barnes S. Dias G. Gagliardi H.-P. Loock N. R. Trefiak H. Waechter S. Yam 《Applied physics. B, Lasers and optics》2009,96(1):193-200
Multi-exponential decay waveforms are common occurrences in cavity ring-down spectroscopy and the respective ring-down times
are typically obtained by fitting the ring-down waveform to the sum of exponential decay functions. In phase-shift cavity
ring-down (CRD) spectroscopy the measurement of a single phase angle will not provide sufficient information and needs to
be complemented by either intensity measurements or phase angle measurements at different modulation frequencies. Here, a
formalism analogous to that developed for fluorescence lifetime spectroscopy is adapted to the phase-shift CRD technique and
is tested for two types of waveguide CRD systems: (1) a single-mode fiber cavity in which light is confined by two identical
Fiber Bragg Gratings and (2) a multimode fiber loop. By measuring the phase angle at different modulation frequencies, lifetimes
for up to three different decay processes were obtained. 相似文献
10.
Nadezhda V. Usol'tseva Olga B. Akopova Antonina I. Smirnova Maria I. Kovaleva Natalia V. Bumbina Nataliia V. Zharnikova 《Phase Transitions》2017,90(8):800-807
ABSTRACTTwo series of star-shaped discotic compounds (A and B) were studied to establish the relationship between their molecular structure and mesogenity. Series A included 19 three-arm compounds with known mesomorphism. Series B consisted of 132 new compounds with unknown mesomorphism: pyromellitic and cyanuric acid derivatives, 5,5′-azo-bis-isophthalic and 4,4′-azodiphthalic acids and triphenylene derivatives. The columnar mesomorphism prediction data for both series were obtained using the original program СМР ChemCard. The prediction data for series A are in good agreement with the experimental results and the reliability of the prediction was estimated to be 89.5%. The same method was applied for series B. The prediction results were approved by the synthesis of individual representatives of series B. A good correlation of the prediction with the experimental data was revealed. 相似文献
11.
We theoretically investigate the spectral measurement errors that are apt to occur in continuous wave (CW) cavity ringdown (CRD) techniques suffering intracavity Doppler shifts. In the typical CW CRD scheme based on a cavity sweep operation for the resonant coupling of a probe laser into a ringdown cavity, the intracavity probe light detunes gradually over time, carrying time-dependent loss information of an absorption feature. Frequency-drifting ringdown signals are theoretically modelled and found to result in erroneous absorption spectra that exhibit the frequency shift of absorption profiles as well as linewidth broadening. PACS 42.62.Fi; 42.60.Da; 42.25.BS 相似文献
12.
The cavity ring down (CRD) technique presented here involves an optical cavity attached to a cryostat. The static cell and
mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of
the cell can be changed between 77 K and 298 K. An off-axis alignment of the laser beam into the cavity is used to increase
the number of resonant modes inside the cavity and improve the signal to noise ratio of the absorption bands. To demonstrate
the capabilities of the low temperature CRD cell, the absorption spectra of O2 are recorded at 90 K for the A (υ′=0←υ″=0) and γ (υ′=2←υ″=0) bands of the b1?g +? X3?g -b^{1}\sum_{g}^{ +}\leftarrow X^{3}\sum_{g}^{ -} transition using cavity ring down spectroscopy. The optical cavity performance was tested using two variations of the CRD
technique. The A-band is measured using the phase-shift cavity ring down method and the γ-band using the pulsed-laser exponential-decay method. A comparison between experimental and simulated spectra of the O2 bands at 90 K confirms the molecular temperature measured by a sensor localized in the cell. Quantitative measurements of
the individual rotational line intensities are made for the oxygen γ-band to confirm the temperature of the cell and calculate the vibrational band intensity. The application of this technique
for laboratory studies of planetary atmospheres and the spectroscopy of molecular complexes is emphasized. 相似文献
13.
Lamia Kara Zaitri 《Molecular physics》2020,118(4)
The molecular structures, linear and nonlinear optical properties of a series constituted by four R-substituted thiophene imino dyes, namely A(R?=?SO2Me), B(R?=?SO2Ph), C(R?=?NO2), and D(R?=?C2(CN)3) were analysed using CAM-B3LYP, ωB97XD and LC-ωPBE hybrid DFT functionals in combination of the 6-311++G(d,p) standard basis set. The dipole moments, polarisabilities, HOMO-LUMO energy gaps, maximum absorption wavelengths and first hyperpolarisabilities were calculated in the gas phase and the obtained results are in good agreement with experimental NLO activity order A?<?B?<?C. Compared to synthesised dyes A-C, the designed dye D presents a longer maximum absorption wavelength and a lower HOMO-LUMO gap because of the appreciable stabilisation of its LUMO energy. These results were confirmed by the calculation of the total second-order stabilisation energy E(2) defined in the context of the NBO population analysis. Consequently, dye D is predicted to exhibit a higher first hyperpolarisability in comparison with dyes A-C. This result can be justified by the enhanced intramolecular charge transfer in dye D due to the stronger electron-withdrawing ability and the cumulative action of the long π-conjugation of the tricyanovinyl moiety. The very high total hyperpolarisability (27 times greater than that of para-nitroaniline) of the designed dye D suggests its promising use in organic NLO devices. 相似文献
14.
Munmun Bardhan Paulami Mandal Wen-Bih Tzeng Tapan Ganguly 《Journal of fluorescence》2010,20(5):1061-1068
By using electrochemical, steady state and time resolved (fluorescence lifetime and transient absorption) spectroscopic techniques,
detailed investigations were made to reveal the mechanisms of charge separation or forward electron transfer reactions within
the electron donor phenothiazine (PTZH) or phenoxazine (PXZH) and well known electron acceptor 9-cyanoanthracene (CNA). The transient absorption spectra suggest that the charge separated species formed in the excited singlet state resulted from
intermolecular photoinduced electron transfer reactions within the donor PTZH (or PXZH) and CNA acceptor relaxes to the corresponding triplet state. Though alternative mechanisms of via formations of contact neutral radical
by H-transfer reaction have been proposed but the observed results obtained from the time resolved measurements indicate that
the regeneration of ground state reactants is primarily responsible due to direct recombination of triplet contact ion-pair
(CIP) or solvent-separated ion-pair (SSIP). 相似文献
15.
T. M. Pradeep Vinayakaprasanna N. Hegde N. Pushpa Ambuj Tripathi K. Asokan 《辐射效应与固体损伤》2013,168(9-10):859-872
ABSTRACTThe pre- and post-irradiation effects on the DC electrical characteristics of 100?MeV Phosphorous (P7+) and 80?MeV Nitrogen (N6+) ion-irradiated NPN transistors were studied in the dose range from 600?krad (Si) to 100?Mrad (Si). The different electrical characteristics, such as Gummel characteristics, excess base current (ΔIB?=?IB-Post?–?IB-Pre), current gain (hFE), damage constant (K) and output characteristics, were measured in situ after ion irradiation. The considerable increase in the base current (IB) at lower VBE and slight decrease in the collector current (IC) at higher VBE were observed after ion irradiation. The C–V measurements revealed that the doping concentration (Nd) was found decreased, while the built-in potential (Vbi) increased after irradiation. The ion-irradiated results are compared with 60Co gamma-irradiated results in the same dose range. The SRIM simulation was performed to understand the range of ions and energy loss in the transistor structure. The SRIM simulation showed that 100?MeV P7+ and 80?MeV N6+ ions can easily pass through the active region of transistors by creating ionization and displacement damages in the device structure. The irradiation results showed that ions induce more degradation in the electrical characteristics when compared to 60Co gamma radiation at the same dose range. 相似文献
16.
S.I. Themelis Y. Komninos C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):277-293
This paper discusses theory and results on 1P0 doubly excited states (DES) in He and in H- of very high excitation, up to the N
= 25 manifold. Our calculations employed full configuration interaction (CI) with large hydrogenic basis sets and produced correlated
wavefunctions for the four lowest roots at each hydrogenic manifold by excluding open channels and the small contribution
of series belonging to lower thresholds. The suitability of the hydrogenic basis sets for such calculations is justified,
apart from their practicality, by the fact that, by computing from them natural orbitals, the results were shown to be the
same with those of earlier multiconfigurational Hartree-Fock (MCHF) calculations on low-lying DES. In total, 160 states were
computed, most of them for the first time. Their energy spectrum should be of use to possible future photoabsorption experiments.
For certain low-lying DES up to N
= 13, for which previous reliable results are available, comparison of the calculated energies shows good agreement. The correlated
wavefunctions contain systematically chosen single and double excitations from each hydrogenic manifold of interest. From
their analysis, we determined the “goodness" of different quantum numbers and the geometry (average angles and radii) as a
function of excitation. For the Sinano lu-Herrick (
K
,
T
) classification scheme, whose basis is a restricted CI with hydrogenic functions and which has thus far been tested only on
low-lying DES, we established that, whereas T remains a good index as energy increases, K does not. Consequently, a more flexible than K quantum number is needed in order to account for most of the additional correlation. This number, represented by F
=
N
-
K
- 1, where N and K are not good numbers anymore, produces consistently a much higher degree of purity than the (
K
,
T
) scheme does, especially as N increases and as the relative significance of various virtual excitations due to electron correlation increases. Among the
four states of each manifold, in all cases in H- and in most cases in He, the three are of the intrashell type and one is of the intershell type with (
F
,
T
) = (0, 0). The lowest intrashell states and the lowest intershell states exhibit a wide angle geometry tending to 180
°
as N
↦∞.
Received 10 September 2001 and Received in final form 12 November 2001 相似文献
17.
We have evaluated the chemical, photophysical and photostability properties of 5,9-diaminodibenzo[a,j]phenoxazinium chloride,
3, and its bis-5,9-ethylamino analogue, 4, with the goal of determining if they have characteristics that are compatible with the requirements of a useful fluorescent
probe. In order to gauge the potential utility of these fluorophores in biological and non-biological applications, these
data were compared to those obtained for Oxazine 118, 1, and Cresyl Violet, 2, two well known fluorescent dyes that differ in molecular structure from the title dye 3 by having two or one fewer benzo moieties fused to a generic oxazine ring structure, respectively. The findings of this investigation
show that 3, as well as bis-ethylamino analogue, 4, have fluorescent lifetimes, quantum yields and photostabilities that compare favorably with the lower order benchmark fluorophores
1 and 2. Moreover, both dibenzo dyes have the highly desirable properties of absorbing and emitting further in the red and far red
/near infrared spectral region, respectively, than do their less conjugated analogues. Taken together, these results suggest
that 3 constitutes an archetype upon which a new class of long wavelength fluororescent reporters might be based. 相似文献
18.
L.A. Errico M. Rentería A.F. Pasquevich A.G. Bibiloni K. Freitag 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):149-156
The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er
2
O
3
and Gd
2
O
3
. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er
2
O
3
) and 300-1173 K (in the case of Gd
2
O
3
). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were
attributed to the electric-field gradients (EFG) acting on 181Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG
results are compared with predictions of the point-charge model and discussed together with previous results obtained with
the probes 111Cd and 181Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed
in terms of dilatometric expansion data.
Received 29 December 2000 and Received in final form 8 March 2001 相似文献
19.
M. Jochum H.-G. Unruh 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):163-168
Dielectric and Raman spectroscopic measurements have been performed to investigate the ferroelectric phase transition in . Single crystals were grown by the zone melting method. The frequency dependence of the dielectric permittivity from 1 MHz
to 1 GHz has been studied in a temperature range between 265 and 285 K. A Debye like dielectric dispersion was found, showing
a critical slowing down around K. Polarized Raman spectra have been taken between 220 and 310 K. Two softening modes have been found, one of A- and another one of B
/
B
g-symmetry. The phase transition mechanism in can be classified as partially order-disorder and partially displacive, confirming former structural results. It resembles
strongly that of monoclinic .
Received: 7 April 1998 / Revised: 5 June 1998 / Accepted: 16 June
1998 相似文献
20.
ABSTRACTThe electro-optical Kerr effect and pre-transition behavior have been investigated for different concentration of dimethyl-aminoazobenzene dye-doped nematic liquid crystal by using the nulled intensity method. Measurement results have showed that the molecular reorientation of liquid crystals induced by photoisomerization of azo dyes come about to increase an amount of Kerr constant at low percentages of dye concentration. Additionally, the results of pre-transition temperature which were obtained by extrapolating the invers Kerr constant as a function of temperature have been found to be in good agreement with predictions of the Landau-De Gennes model. 相似文献