Millisecond experiments

In transient absorption measurements the number of probing photons in the time window of interest should be sufficiently large to get a satisfactory signal to noise SIN) ratio. For instance, in a nanosecond experiment the number of photons during 1 nsec should preferably be similar to the number of photons during a millisecond experiment. For this reason a continuous lamp can be used as a probe source in the latter experiment, whereas a flash lamp is preferred in the former. 

Millisecond experiments can be used to determine thermal and electrical properties of metals and alloys in the solid phase up to the melting point at around 3000 K. This moderately fast heating rate allows, e.g., the determination of phase transition temperatures. Nevertheless, millisecond e eriments are limited to the solid state as the rate of heating is still slow compared to the gravitational collapse of a liquid sample under gravitational forces once it becomes molten. Another limitation from the moderate heating rate is the need for heat loss corrections at elevated temperatures. 

Besides measurements of thermophysical properties, millisecond experiments are the tools of choice for metrological investigations. They have been used by NIST, USA INRiM, Italy NRLM, Japan and lately by HIT, China, for measurements dealing with radiance temperatures, radiometry, and total hemispherical emittance measurements [10,11]. 

Temperature either by contact thermometry (millisecond experiments only) or surface radiation for optical thermometry, J(t)... 

Institute [52]. Although interferometric techniques may lead to higher measurement accuracy, the instruments are mostly restricted to the solid state and to millisecond experiments. ... 

However, data in the solid state obtained with millisecond experiments are more accurate than data from this combined ps/DSC-experiment. Nevertheless, this combination was designed for using the existing instrumentation at TUG. 

The striker was fabricated in accordance wifli ISO 179 and contains strain gages located near the point of impact. The instrumented system is a Tinius Olsen system v2.1 which is capable of measuring any number of data points up to 19,000 per test. The time scale can be set at any range from 20 microseconds to 20 seconds, however, most impact tests have a duration ranging from about 0.5 milliseconds to 20 milliseconds. Experience in metals testing [1] has shown that at least 500 data points per millisecond are needed to accurately characterize the dynamic portions of the load-time curve. It is recommend that instrumented impact tests be conducted using 500 to 1000 data points per millisecond. 

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

One of the major limiting factors for the time resolution of flow-hibe experiments is the time required for mixing reactants and—to a lesser extent—the resolution of distance. With typical fast flow rates of more than 25 ms [42, 43] the time resolution lies between milliseconds and microseconds. 

This result reflects the Kramers relation (Gardiner, 1985). A millisecond time of unbinding, i.e.. Tact 1 ms, corresponds in this case to a rupture force of 155 pN. For such a force the potential barrier AU is not abolished completely in fact, a residual barrier of 9 kcal/mol is left for the ligand to overcome. The AFM experiments with an unbinding time of 1 ms are apparently functioning in the thermally activated regime. 

Fig. 5. Theory vs. experiment rupture forces computed from rupture simulations at various time scales (various pulling velocities Vcant) ranging from one nanosecond (vcant = 0.015 A/ps) to 40 picoscconds (vcant = 0.375 A/ps) (black circles) compare well with the experimental value (open diamond) when extrapolated linearly (dashed line) to the experimental time scale of milliseconds.

The previous application — in accord with most MD studies — illustrates the urgent need to further push the limits of MD simulations set by todays computer technology in order to bridge time scale gaps between theory and either experiments or biochemical processes. The latter often involve conformational motions of proteins, which typically occur at the microsecond to millisecond range. Prominent examples for functionally relevant conformatiotial motions... 

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

Laboratory experiments have shown that reaction 15 occurs on ice in the absence of HCl (11-13) furthermore, the product HOCl appears on a time scale of minutes, in contrast to CI2 in reaction 13, which is produced on at most a millisecond time scale (11). Thus, in this mechanism HOCl serves as an intermediate if there is enough HQ on the ice, HOCl will react with HCl while still on the ice surface otherwise the HOCl will desorb, eventually finding an HCl molecule in the ice, perhaps after several adsorption-desorption cycles. 

The two-pulse TR experiments allow one to readily follow the dynamics and structural changes occurring during a photo-initiated reaction. The spectra obtained in these experiments contain a great deal of information that can be used to clearly identify reactive intermediates and elucidate their structure, properties and chemical reactivity. We shall next describe the typical instrumentation and methods used to obtain TR spectra from the picosecond to the millisecond time-scales. We then subsequently provide a brief introduction on the interpretation of the TR spectra and describe some applications for using TR spectroscopy to study selected types of chemical reactions. 

Since there are a large number of different experimental laser and detection systems that can be used for time-resolved resonance Raman experiments, we shall only focus our attention here on two common types of methods that are typically used to investigate chemical reactions. We shall first describe typical nanosecond TR spectroscopy instrumentation that can obtain spectra of intermediates from several nanoseconds to millisecond time scales by employing electronic control of the pnmp and probe laser systems to vary the time-delay between the pnmp and probe pnlses. We then describe typical ultrafast TR spectroscopy instrumentation that can be used to examine intermediates from the picosecond to several nanosecond time scales by controlling the optical path length difference between the pump and probe laser pulses. In some reaction systems, it is useful to utilize both types of laser systems to study the chemical reaction and intermediates of interest from the picosecond to the microsecond or millisecond time-scales. 

Since modern FTIR spectrometers can operate in a rapid scan mode with approximately 50 ms time resolution, TRIR experiments in the millisecond time regime are readily available. Recent advances in ultra-rapid scanning FTIR spectroscopy have improved the obtainable time resolution to 5 ms. Alternatively, experiments can be performed at time resolutions on the order of 1-10 ms with the planar array IR technique, which utilizes a spectrograph for wavelength dispersion and an IR focal plane detector for simultaneous detection of multiple wavelengths. ... 

The SPRITE signal equation is identical to Eq. (3.4.1) and it is possible to acquire density weighted images in the same manner as an SPI experiment. The TR in a SPRITE experiment is only a few milliseconds, which is similar to the Tj of a concrete specimen. Therefore to remove this influence from the image, a can be... 

The resolution of the zeolite MR image is 100 x 100 x 100 gm3 and has therefore reached the resolution limit that defines NMR microscopy. For the instrumentation used for this experiment, it will take at least a few milliseconds due to the ramping time of the field gradients. If the mean displacement of the xenon atoms during this experimental time scale reaches the dimension of the voxels or pixels, the resolution limit is reached. For instance, for the aerogel experiments in Figure... 

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