Sapphire run

The time constants are determined by running a baseline in an empty cell (i.e., without the sample pan and the reference pan), while the thermal capacitance is calculated using a sapphire run two similar mass sapphire disks are placed on the sample and reference platforms, and heated at the same rate as the above mentioned baseline run. The thermal resistance is defined as the time constant divided by the thermal capacitance. Three modes are possible for the QIOOO and Q2000 DSCs ... 

With such heat capacity determination it would take a long time to determine temperature dependence of the heat capacity. However, the curves from Ti to steady state and steady state to T2 have similar shape therefore the hs-u (for sample and baseline) amplitude differences are proportional to the heat capacity at every temperature and there is no need to determine the Ss-bi area (shaded area in Fig. 2.19a), but simply to measure the /ts-bi amplitude differences. So, if the instrument is calibrated with a standard for which the temperature dependence of the heat capacity is well known, the heat capacity of the sample can be measured at any temperature. For this, the /isap-w amplitude differences must be used (see Fig. 2.19a, curves Sapphire run and Baseline ). The standard is usually sapphire (crystalline AI2O3), which is readily available from the instrument companies. For low-temperature heat capacity... 

First, the zero line is recorded using two empty crucibles. Next, a calibrant substance (usually alumina, i.e., synthetic sapphire) is placed in the sample crucible and the temperature program is repeated. Finally, the calibrant is replaced by the sample under study (keeping the crucible) and the temperature program run a third time. Based on equations 12.20 and 12.21, it can be concluded that the ordinate difference between the traces of the calibrant curve and of the zero line obtained for a given time t leads to the corresponding value of fcp ... 

Femtosecond Ti-Sapphire oscillator (CDP, TiF50, 100 fs, 80 MHz, 0.3 W, 800 run) pumped with diode pumped solid state laser (Coherent, Verdi) was used to excite the system. The time- and spectral-resolved fluorescence spectra of C522 were measured by using up-conversion set-up (CDP, FOG100). The p-cyclodextrin, C42H70O35, and coumarin C522, C14H12F3NO2, used in these experiments were produced by Cyclolab and Radiant Dyes Chemie, respectively. All experiments were performed at room temperature and used water was twice deionised. 

Experimental. All photodimerizations were carried out in a stainless steel fixed volume cell (1.75 cm ID with a 1.0 cm path length) with sapphire windows under the irradiation of a Hanovia medium pressure mercury lamp filtered through water and Pyrex for a 13.5 hour exposure. The cell and lamp assembly have been described previously (31). For selected runs a custom built 0.9 mL variable-volume pump was connected to the cell and the pressure was varied to determine the exact location of the phase boundary, based on light scattering measured in a Cary 2290 UV-Vis spectrophotometer (Varian Inst.). The spectrophotometer was also used to measure the concentrations of the monomeric cyclohexenone before and after reaction. 

The specific heat at constant pressure, Cpf of the HIP-treated sample with nominal composition LaVg 25 0,7504 was measured over the temperature range 4-400 K by the heat pulse method in a calorimeter that incorporates a feedback system to regulate the temperature of concentric radiation shields surrounding the sample (9). The Cp values are accurate to within 1%, as determined by calibration runs using a polycrystalline copper sample and a sapphire single crystal sample. 

Solid state lasers CW or pulsed lasers in which the active medium is a sohd matrix (crystal or glass) doped with an ion (e. g., Nd, Cr, Er ). The emitted wavelength depends on the active ion, the selected optical transition, and the matrix. Some of these lasers are tunable within a very broad range (e.g., from 700 to 1000 run for Ti doped sapphire). 

Different types of set-up have been reported in the literature. A typical transient absorption set-up with a continuum probe and subpicosecond time resolution, which can be used with laser pulses of a few hundred femtoseconds of duration, is shown in Fig. 7.15. The sample is excited by the pump pulses P. The pump flu-ence (number of photons per cm ) is set to be large enough to obtain an appreciable population of the excited state, which however can be small when an excitation source of high repetition rate is used (Ti-sapphire femtosecond lasers run at 1 kHz) because it allows fast accumulation of weak amplitude signals. With low repetition lasers (10 Hz) the excitation fluence should be dose to the saturation fluence ( l/ca, where (7 is the absorption cross section of the solute at the pump wave-... 

An experimental illustration of the study of such objects, made of several polyciystalline films, is shown in Figure 7.7. We reahzed a sample comprised of a titaniirm oxide film placed on top of a zirconia film, all of this deposited on a sapphire substrate. The titaniirm oxide film is roughly 20 run wide and the zirconia film about 50 run wide. Two diffraction patterns obtained with the incidence angles... 

The AFM experiments were performed under ambient conditions with a Topometrix Explorer AFM. The sapphire substrate samples were investigated in contact mode. The organic films were examined in tapping mode in order to decrease the interaction of the tip with the sample. The resolution of the AFM is 50 run in lateral and less than 1 nm in vertical direction. 

Experiments were performed using a titanium sapphire laser oscillator capable of producing pulses with bandwidths up to 80 run FWHM. The output of the oscillator was evaluated to make sure there were no changes in the spectrum across the beam and was compressed with a double prism pair arrangement. The pulse shaper uses prisms as the dispersive elements, two cylindrical concave mirrors, and a spatial light modulator (CRI Inc. SLM-256), composed of two 128-pixel liquid crystal masks in series. The SLM was placed at the Fourier plane [5]. After compression and pulse shaping, 200 pJ pulses were used to interrogate the samples. 

We describe beamline ID09B at the European Synchrotron Radiation Facility (ESRF), a laboratory for optical pump and x-ray probe experiments to 100-picosecond resolution. The x-ray source is a narrow-band undulator, which can produce up to 1 x 10 photons in one pulse. The 3% bandwidth of the undulator is sufficiently monochromatic for most diffraction experiments in liquids. A Ti sapphire femtosecond laser is used for reaction initiation. The laser runs at 896 Hz and the wavelength is tunable between 290-1160 nm. The doubled (400 nm) and tripled wavelength (267 nm) are also available. The x-ray repetition frequency from the synchrotron is reduced to 896 Hz by a chopper. The time delay can be varied from 0 ps to 1 ms, which makes it possible to follow structural processes occurring in a wide range of time scales in one experiment. 

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