Spectral artifacts

There are two types of NOE experiments that can be performed. These are referred to as the steady-state NOE and the transient NOE. The steady-state NOE experiment is exemplified by the classic NOE difference experiment [15]. Steady-state NOE experiments allow one to quantitate relative atomic distances. However, there are many issues that can complicate their measurement, and a qualitative interpretation is more reliable [16]. Spectral artifacts can be observed from imperfect subtraction of spectra. In addition, this experiment is extremely susceptible to inhomogeneity issues and temperature fluctuations. 

The spectral quality and the efficiency of the basic COSY and the DQ-filtered COSY experiments may be improved with the use of field gradients instead of phase cycling for coherence selection, which remove spectral artifacts and make time consuming phasecycling superfluous. 

Reload the same 2D raw data set. use the same basic processing parameters as above, but now set in the F1 Processing parameters list MEmod to LPfc and NCOEF to 8. Process the data the same way as above, store the 2D spectrum and the same columns numbers. Use the Multiple display option in ID WIN-NMR to compare corresponding columns with respect to signal-to-noise. resolution and spectral artifacts. 

Finally, we wish to report the results for simulated cell smears. These experiments are being carried out to determine the best parameters for data acquisition, and to establish the variations of the cellular spectra from a homogeneous cell culture. Similar efforts have been undertaken before, where the cells were spin-deposited onto the microscope slides. However, for cultured cervical cancer (HeLa) cells, the resulting samples contained many cells that maintained their morphology in suspension quite well, and produced dried cells that were nearly spherical. Once dried, these cells could not be stained easily, and thus, their divisional activity could not be established after IR data acquisition. Furthermore, large spherical cells often gave spectral artifacts that made interpretation impossible.16... 

A consistent protocol for the collection and analysis of thin-film EDS data requires an assessment of both instrument and specimen dependent parameters. Major parameters which should be considered for thin-film analyses include spurious X-rays, spectral artifacts, detector geometry, probe diameter, beam broadening, contamination, sample preparation artifacts, sample orientation and temperature and X-ray absorption. Many of these parameters are interdependant during an analysis and the prudent operator will evaluate as many as possible before routine use of an AEM. Further explanations of these parameters can be found in a number of publications [4,6.,9.,7] Only selected parameters are discussed below. 

THz spectra. As an example, there are discrepancies in the reported THz spectra of RDX [38,39,90]. In addition, the experimental method itself can introduce spectral artifacts that can mask the true THz spectral fingerprint. These include multiple reflections within the sample, multiple reflections between the sample and its holder, and multiple reflections from the system, etc. [13]. 

An early alternative to soft pulses was the DANTE Delays Alternating with Nutation for Tailored Excitation) experiment, which used a sequence of short, hard pulses of angle a <3C 90°, followed by a fixed delay t to achieve selective excitation. Thus, the pulse sequence is (a-T), ]. Nuclei that are on resonance are eventually driven to the y axis and hence are selected, whereas those more removed from the frequency range are not affected. The sequence of hard pulses can achieve a result similar to that of soft pulses and even can be shaped by modulating the duration of the pulse lengths, but DANTE pulses lead to spectral artifacts not created by soft pulses, such as unwanted sidebands. 

Adhering to these rather strict requirements for optimal optical density, spectral range and minimizing spectral artifacts requires permanent verifications of the reality of the CD signal measured. Good CD results require formulation and keeping of the measurement protocol. It is recommended that the vhole series of samples that are to be compared is measured under the same conditions. For example, a broken sample cell can distort the vhole series. 

The analysis of NMR spectra involves intensive human intervention, and automation of NMR spectroscopy with macromolecules is thus of general interest. Major challenges are the distinction of real resonance peaks from thermal noise and spectral artifacts, as well as peak overlap [34—36]. On grounds of principle, automated analysis benefits from higher-dimensionality of the spectra [21, 37], since the peaks are then more widely separated, and hence peak overlap is substantially reduced. 

For arbitrary, non-uniform sampling it is no longer possible to obtain a spectrum that is equal to a spectrum of continuous signal, even if it is strictly band-limited. Spectral artifacts, depending on the sampling schedule, appear as part of Point Spread Function. 

Conventional (Cartesian grid) sampling as a scheme is an obvious method of choice, when experimental time and/or line width expense is acceptable. However, when especially narrow spectral lines or high dimensionality are required, irregular sampling should be employed. As stated above, it can make peak widths independent of experimental time. Nevertheless, one should always remember about cost of irregularity, i.e., introduction of spectral artifacts, whose pattern and level is dependent on a sampling scheme. 

Not surprisingly, it appears that one can use discrete FT spectrum to find the most probable sources of spectral artifacts. 

Transmitter glitch. A small spectral artifact often observed in the very center of the spectral window that is caused by a small amount of the RF generated in the console getting through to the receiver. 

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