26 research outputs found
On the minimum phase property of prediction-error polynomials
We provide a simple proof of the minimum phase property of the optimum linear prediction polynomial. The proof follows directly from the fact that the minimized prediction error has to satisfy the orthogonality principle. Additional insights provided by this proof are also discussed
Localizing triplet periodicity in DNA and cDNA sequences
<p>Abstract</p> <p>Background</p> <p>The protein-coding regions (coding exons) of a DNA sequence exhibit a triplet periodicity (TP) due to fact that coding exons contain a series of three nucleotide codons that encode specific amino acid residues. Such periodicity is usually not observed in introns and intergenic regions. If a DNA sequence is divided into small segments and a Fourier Transform is applied on each segment, a strong peak at frequency 1/3 is typically observed in the Fourier spectrum of coding segments, but not in non-coding regions. This property has been used in identifying the locations of protein-coding genes in unannotated sequence. The method is fast and requires no training. However, the need to compute the Fourier Transform across a segment (window) of arbitrary size affects the accuracy with which one can localize TP boundaries. Here, we report a technique that provides higher-resolution identification of these boundaries, and use the technique to explore the biological correlates of TP regions in the genome of the model organism <it>C. elegans</it>.</p> <p>Results</p> <p>Using both simulated TP signals and the real <it>C. elegans </it>sequence F56F11 as an example, we demonstrate that, (1) Modified Wavelet Transform (MWT) can better define the boundary of TP region than the conventional Short Time Fourier Transform (STFT); (2) The scale parameter (a) of MWT determines the precision of TP boundary localization: bigger values of a give sharper TP boundaries but result in a lower signal to noise ratio; (3) RNA splicing sites have weaker TP signals than coding region; (4) TP signals in coding region can be destroyed or recovered by frame-shift mutations; (5) 6 bp periodicities in introns and intergenic region can generate false positive signals and it can be removed with 6 bp MWT.</p> <p>Conclusions</p> <p>MWT can provide more precise TP boundaries than STFT and the boundaries can be further refined by bigger scale MWT. Subtraction of 6 bp periodicity signals reduces the number of false positives. Experimentally-introduced frame-shift mutations help recover TP signal that have been lost by possible ancient frame-shifts. More importantly, TP signal has the potential to be used to detect the splice junctions in fully spliced mRNA sequence.</p
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Skin model surface temperatures during single and multiple cryogen spurts used in laser dermatologic surgery.
BackgroundAlthough cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery, concern has been expressed that CSC may induce cryo-injury. In order to address this concern, it is necessary to evaluate the effects of prolonged exposure of human skin phantoms (HSP) to CSC.ObjectiveTo measure the minimum surface temperature (T(min)) and the time at which it occurs (t(Tmin)) as well as determine the time the sprayed HSP surface remains below 0 degrees C (sub-zero time, Deltat(s)) and -26 degrees C (residence time, Deltat(r)) during the application of single (SCS) and multiple (MCS) cryogen spurts. Two initial HSP substrate temperatures were studied, T(i): 23 and 70 degrees C.Study design/materials and methodsAn epoxy-based HSP was constructed to measure T(min), t(Tmin), Deltat(s), and Deltat(r), for 17 spray patterns: 1 SCS with a total cryo-delivery time (Deltat(c)) of 40 milliseconds; 8 MCS patterns with identical Deltat(c), but with a total cooling time (Deltat(total)) varying from 50 to 280 milliseconds; and 8 SCS patterns that matched the Deltat(total) of the MCS patterns.ResultsFor both T(i), our results show that it is possible to distinguish between two different cooling regimes. For Deltat(total) ConclusionsThese results suggest that: (1) similar epidermal protection may be attained with SCS and MCS for Deltat(total
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Evaluation of tissue effects after continuous versus shorter multiple intermittent cryogen spray cooling exposure
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Evaluation of single versus multiple cryogen spray cooling spurts on in vitro model human skin.
Many commercially available dermatologic lasers utilize cryogen spray cooling for epidermal protection. A previous tissue culture study demonstrated that single cryogen spurts (SCS) of 80 ms or less were unlikely to cause cryo-injury in light-skinned individuals. More recently, multiple cryogen spurts (MCS) have been incorporated into commercial devices, but the effects of MCS have not been evaluated. The aim was to study an in vitro tissue culture model and the epidermal and dermal effects of SCS vs patterns of shorter MCS with the same preset total cryogen delivery time (Deltat(c)) and provide an explanation for noted differences. Four different spurt patterns were evaluated: SCS: one 40-ms cryogen spurt; MCS2: two 20-ms cryogen spurts; MCS4: four 10-ms cryogen spurts; MCS8: eight 5-ms cryogen spurts. Actual Deltat(c) and total cooling time (Deltat(Total)) were measured for each spurt pattern. RAFT tissue culture specimens were exposed to cryogen spurt patterns and biopsies were taken immediately and at days 3 and 7. Actual Deltat(c) was increased while Deltat(Total) remained relatively constant as the preset Deltat(c) of 40 ms was delivered as shorter MCS. Progressively more epidermal damage was noted with exposure to the MCS patterns. No dermal injury was noted with either SCS or MCS. For a constant preset Deltat(c) of 40 ms, delivering cryogen in patterns of shorter MCS increased the actual Deltat(c) and consequently the observed epidermal cryo-injury as compared to an SCS