Irregular Segments Research Articles

Human health risk assessment for consumption of microplastics and plasticizing substances through marine species

A special characteristic of MP (microplastics) in the ocean is they may act as carriers of additives specific to the plastic materials used in their manufacture, such as plasticizers, among which Bisphenol-A (BPA), bis (2-ethylhexyl) phthalate (DEHP), dybuthyl phthalate (DBP). Both MP as the plasticizers were searched in composite samples of mangrove cockle (Anadara tuberculosa), Stolzmann's weakfish (Cynoscion stolzmanni) and arched swimming crab (Callinectes arcuatus). Extraction of MP was done through physical-chemical techniques and identification was carried out employing the techniques of light microscopy, energy dispersive spectrometer (EDS), scanning electron microscope (SEM) and Raman spectroscopy; the sizes of MP obtained were between 0.5 μm and 106 μm, the following average results being obtained: for Arched swimming crab 4.0 ± 1.0 MP/g; mangrove cockle 3.3 ± 2.9 MP/g; and for Stolzmann's weakfish, the average was 2.4 ± 1.3 MP/g; the most observed shapes were fibers and irregular segments; the most identified MP was polyethylene terephthalate (PET). Regarding extraction and quantification of plasticizers, the extraction stage was carried out using QuEChERS tubes; and the identification and quantification with gas chromatography coupled to a mass spectrometer (GC-MS). Regarding the plasticizing substances, DEHP was found in detectable levels in all the samples; BPA was found in 84% of the composite samples analyzed; DBP was found in 50% of them, of the analyzed samples 34% were positive for the 3 analytes. The dietary exposure of people to plasticizers was calculated and for BPA the exposure obtained was compared with respect to the TDI (tolerable intake dose) for pregnant women and the new TDI proposed by EFSA in 2021 according to the estrogenic effect of this substance in the fetus. The objective of the work was to determine if a relationship could be established between both PM and plasticizers, which gave a positive relationship.

Investigation of Vocal Bifurcations and Voice Patterns Induced by Asymmetry of Pathological Vocal Folds.

Vocal fold asymmetry creates irregular entrainments and modulations in voice, which may lead to rough perceptual quality. The presence of asymmetry can also cause mid-phonation bifurcations where a small change in the phonatory system causes a drastic change in vibration pattern, resulting in transitions in and out of rough voice. This study surveys sustained phonation recordings of speakers with the diagnoses of vocal fold polyp or unilateral vocal fold paralysis to investigate the resulting voice patterns. This retrospective study observed 71 sustained phonation recordings from 48 patients. Segments with distinctive signal patterns were identified within each recording with narrowband spectrogram and computer-assisted analysis of spectral peaks. Phonation segmentation yielded 240 segments across all the recordings. Five voice patterns were recognized: (regularly or irregularly) entrained, modulated, uncoupled, unstable, and pulsed. Thirty-six patients (75%) exhibited irregular patterns. No single irregular pattern lasted for the entire phonation and was always accompanied by at least one mid-phonation bifurcation. Durations of the irregular segments (M = 0.4 s) were significantly shorter than the segments with the regular pattern (M = 1.4 s). The results suggest that vocal fold pathology frequently introduces dynamic vibratory patterns that affect both the acoustic signals and perceptions. Due to these abnormalities, it is important for clinical voice assessment protocols, both perceptual and acoustic, to account for these possible bifurcations, irregular signal patterns, and their tendencies.

An Effective Machine Learning Approach for Classifying Artefact-Free and Distorted Capnogram Segments Using Simple Time-Domain Features

Capnogram signal analysis has received considerable attention owing to its important applications in assessing cardiopulmonary functions. However, the automatic elimination of deformed parts of a capnogram waveform remains an open research problem. Herein, we introduce an automatic classification approach for discriminating artefact-free (regular) and distorted (irregular) segments of capnogram signals. The proposed features include Hjorth parameters and mean absolute deviation (MAD). The main advantage of these features is their simplicity, such that they can be employed in a computationally efficient machine learning algorithm. MATLAB simulation is conducted on 100 regular and 100 irregular segments of capnogram to extract the proposed and existing features, which are ranked based on the Pearson correlation coefficient, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula> -value and area under receiver operating characteristic (ROC) curve. The naive Bayes, decision tree, random forest and support vector machine (SVM) classifiers are fed by the relatively highly ranked features, and the classification performance is assessed via ten-fold cross-validation. Besides the linear kernel SVM, the radial basis function (RBF) and polynomial kernel functions with different orders are also included in the current experiment. Results revealed the effectiveness of the Hjorth activity and MAD attributes when used with the fourth-order polynomial kernel-SVM classifier. The achieved accuracy, precision and specificity are 89%, 92.1%, and 91% outperforming the existing method by 2.5%, 5.6% and 7%, respectively. The simplicity of the proposed time-domain features is confirmed by the average total computational time of features extraction and classification phases which is only 13 ms instead of 19 ms in the case of incorporating both time- and frequency-domain features, indicating a reduction of 31.6%. It is envisaged that the proposed approach can be valuable if implemented with capnography devices for real-time and fully automated capnogram-based respiratory assessment. Even so, further research is recommended to enhance the classification performance through exploring more features and/or classifiers.

A bio-inspired B-Spline Offset Feature for structural topology optimization

In this paper, we propose a B-Spline Offset Feature (BSOF) for feature-driven topology optimization. The feature is inspired from the geometric morphology of worms characterized by an elongated cylindrical, bilaterally symmetric, and well-segmented body along a highly deformable directrix. B-spline is used to define the directrix with its outward and inward offsets outlining the BSOF. This definition endows the BSOF with high deformability such as self-folding and self-intersection. To construct the implicit level-set function (LSF), the BSOF is decomposed into a sequence of segments whose LSFs can easily be constructed by Kreisselmeier–Steinhauser (KS) function. Regular or irregular shaped segments are identified by the deformation gradient. Irregular segments involving geometrical singularities, e.g. distorted and concave segments, are replaced with convex hulls. The stiffest structure design and compliant mechanism synthesis are studied to illustrate the effectiveness and advantages of the proposed BSOF for topology optimization.

A mechanical model of early somite segmentation

SummarySomitogenesis is often described using the clock-and-wavefront (CW) model, which does not explain how molecular signaling rearranges the pre-somitic mesoderm (PSM) cells into somites. Our scanning electron microscopy analysis of chicken embryos reveals a caudally-progressing epithelialization front in the dorsal PSM that precedes somite formation. Signs of apical constriction and tissue segmentation appear in this layer 3-4 somite lengths caudal to the last-formed somite. We propose a mechanical instability model in which a steady increase of apical contractility leads to periodic failure of adhesion junctions within the dorsal PSM and positions the future inter-somite boundaries. This model produces spatially periodic segments whose size depends on the speed of the activation front of contraction (F), and the buildup rate of contractility (Λ). The Λ/F ratio determines whether this mechanism produces spatially and temporally regular or irregular segments, and whether segment size increases with the front speed.

Fusing simulated GEDI, ICESat-2 and NISAR data for regional aboveground biomass mapping

Accurate mapping of forest aboveground biomass (AGB) is critical for better understanding the role of forests in the global carbon cycle. NASA's current GEDI and ICESat-2 missions as well as the upcoming NISAR mission will collect synergistic data with different coverage and sensitivity to AGB. In this study, we present a multi-sensor data fusion approach leveraging the strength of each mission to produce wall-to-wall AGB maps that are more accurate and spatially comprehensive than what is achievable with any one sensor alone. Specifically, we calibrate a regional L-band radar AGB model using the sparse, simulated spaceborne lidar AGB estimates. We assess our data fusion framework using simulations of GEDI, ICESat-2 and NISAR data from airborne laser scanning (ALS) and UAVSAR data acquired over the temperate high AGB forest and complex terrain in Sonoma County, California, USA. For ICESat-2 and GEDI missions, we simulate two years of data coverage and AGB at footprint level are estimated using realistic AGB models. We compare the performance of our fusion framework when different combinations of the sparse simulated GEDI and ICEsat-2 AGB estimates are used to calibrate our regional L-band AGB models. In addition, we test our framework at Sonoma using (a) 1-ha square grid cells and (b) similarly sized irregularly shaped objects. We demonstrate that the estimated mean AGB across Sonoma is more accurately estimated using our fusion framework than using GEDI or ICESat-2 mission data alone, either with a regular grid or with irregular segments as mapping units. This research highlights methodological opportunities for fusing new and upcoming active remote sensing data streams toward improved AGB mapping through data fusion.

Identifying and Grouping Abnormalities in Medical Images using Shortest Path Algorithms

The majority of the patient conclusion rotates around in distinguishing variations from the norm in their particular restorative pictures. These pictures are of different kinds, likely Ultrasound, CT Scan, MRI and infinitesimal pictures like bio-synthetic slides, smaller scale organic slides and neurotic slides. Barely any irregularities are cracks, awful cells in blood, tumors, contagious recognizable proof and so on. Finding the unusual segments, abnormalities in these pictures needs aptitude by the doctor; this adept recognizable proof advances and ensures sound drug by the doctor or specialist to persistent. In medicinal infinitesimal pictures ordinary bits and strange segments are combined. None of the irregular segments are identified with strange and typical parts of picture for example deviations are dissipated among ordinary bits of picture. These deviations are absent in certain bits for explicit region in the pictures. None of these deviations are covered nor can be gathered into a solitary segment physically in the picture. Deviations can be segregated alongside typical segments of pictures. Recognizing such deviations incompletely goes under bunching. This venture recognizes deviations in Medical Microscopic pictures. These deviations can be distinguished outwardly which uncovers about the nearness of deviation however to know the level of deviation in an example picture is basic. So as to accomplish this all deviations must be associated. This task interfaces all deviations utilizing Shortest Path calculation and bunches utilizing Hierarchical Clustering calculations.

A temporal visualization of chronic obstructive pulmonary disease progression using deep learning and unstructured clinical notes

BackgroundChronic obstructive pulmonary disease (COPD) is a progressive lung disease that is classified into stages based on disease severity. We aimed to characterize the time to progression prior to death in patients with COPD and to generate a temporal visualization that describes signs and symptoms during different stages of COPD progression.MethodsWe present a two-step approach for visualizing COPD progression at the level of unstructured clinical notes. We included 15,500 COPD patients who both received care within Partners Healthcare’s network and died between 2011 and 2017. We first propose a four-layer deep learning model that utilizes a specially configured recurrent neural network to capture irregular time lapse segments. Using those irregular time lapse segments, we created a temporal visualization (the COPD atlas) to demonstrate COPD progression, which consisted of representative sentences at each time window prior to death based on a fraction of theme words produced by a latent Dirichlet allocation model. We evaluated our approach on an annotated corpus of COPD patients’ unstructured pulmonary, radiology, and cardiology notes.ResultsExperiments compared to the baselines showed that our proposed approach improved interpretability as well as the accuracy of estimating COPD progression.ConclusionsOur experiments demonstrated that the proposed deep-learning approach to handling temporal variation in COPD progression is feasible and can be used to generate a graphical representation of disease progression using information extracted from clinical notes.

MLS POINT CLOUD SEGMENTATION BASED ON FEATURE POINTS OF SCANLINES

Abstract. Point clouds acquired using Mobile Laser Scanning (MLS) are applied to extract road information such as curb stones, road markings, and road side objects. In this paper, we present a scanline-based MLS point cloud segmentation method for various road and road side objects. First, end points of the scanline, jump edge points, and corner points are extracted as feature points. The feature points are then interpolated to accurately extract irregular parts consisting of irregularly distributed points such as vegetation. Next, using a point reduction method, additional feature points on a smooth surface are extracted for segmentation at the edges of the curb cut. Finally, points between the feature points are extracted as flat segments on the scanline, and continuing feature points are extracted as irregular segments on the scanline. Furthermore, these segments on the scanline are integrated as flat or irregular regions. In the extraction of the feature points, neighboring points based on the spatial distance are used to avoid being influenced by the difference in the point density. Based on experiments, the effectiveness of the proposed method was indicated based on an application to an MLS point cloud.

Macro and Microanatomical Structures of Lizard’s Regenerate Tail (Mabouya multifasciata Kuhl, 1820)

Lizards are animals that can do autotomy. Research on the autotomy of lizard’s tail has been carried out, but few have examined about axial skeletons that focus on vertebrae caudales or arranged muscles. That is the background of this research. This research is expected to be a database for further research and as a comparison between animals that can perform other autotomies. This research intend to determine the macro and micro structures of the anatomical axial skeleton lizard’s regenerate tail and to know the micro structures of anatomy muscular segmentation lizard’s regenerate tail. The used methods are X-Ray, Alizarin Red S and Alcian Blue, Paraffin method with Hematoxylin-Eosin and Mallory Triple Strain staining. The result showed that the lizard's regenerate tail was darker than the original. On observations using X-Ray and Alizarin staining showed that the original tail is seen broad and have a Processus. The original lizard's tail is composed of bones, because it is red which shows perfectly calcified bones. While the regenerate of the lizard's tail is composed of bones in the form of long pipes which are red-colored because they have calcified from outside. Muscular segmentation of the original lizard's tail when viewed transversely has irregular segments. While the lizard's regenerate tail has 15 muscle segments. Muscles are composed of a collection of myotubes that become myotomes, each of myotomes confined by the myoseptum.

Leonophyllum tenellum nov. gen., nov. sp., an enigmatic plant from the Early Jurassic of the Mecsek Mts (Hungary)

The Early Jurassic flora of the Mecsek Mountains is diverse, with numerous representatives of ferns, seed ferns, cycadophytes, ginkgophytes, and conifers. Its (para-)autochthonous deposition, good preservation and low collection bias has permitted researchers to save delicate, small plant remains that would generally be missing from the fossil record. These plant fossils are characterized by having a “filmy” (probably unilayered) structure, thin stalks with flat leaf-like branches and ultimate irregular segments with streamlined epidermal cells having thick cell walls. Due to the absence of sporangia, the plant remains cannot be confidently assigned to any higher plant group, although they show some similarities to thalloid liverworts with raised vegetative bodies and also have some resemblance to the fern family Hymenophyllaceae. The new genus and species Leonophyllum tenellum Barbacka et Kustatscher is erected.

A Compressed Chain Code Based on Irregular Line Segments Combination

A Compressed Chain Code Based on Irregular Line Segments Combination

Performance of a multi leaf collimator system for MR-guided radiation therapy.

The purpose of this study was to investigate and characterize the performance of a Multi Leaf Collimator (MLC) designed for Cobalt-60 based MR-guided radiation therapy system in a 0.35 T magnetic field. The MLC design and unique assembly features in the ViewRay MRIdian system were first reviewed. The RF cage shielding of MLC motor and cables were evaluated using ACR phantoms with real-time imaging and quantified by signal-to-noise ratio. The dosimetric characterizations, including the leaf transmission, leaf penumbra, tongue-and-groove effect, were investigated using radiosensitive films. The output factor of MLC-defined fields was measured with ionization chambers for both symmetric fields from 2.1 × 2.1 cm2 to 27.3 × 27.3 cm2 and asymmetric fields from 10.5 × 10.5 cm2 to 10.5 × 2.0 cm2 . Multi leaf collimator (MLC) positional accuracy was assessed by delivering either a picket fence (PF) style pattern on radiochromic films with wire-jig phantom or double and triple-rectangular patterns on ArcCheck-MR (Sun Nuclear, Melbourne, FL, USA) with gamma analysis as the pass/fail indicator. Leaf speed tests were performed to assess the capability of full range leaf travel within manufacture's specifications. Multi leaf collimator plan delivery reproducibility was tested by repeatedly delivering both open fields and fields with irregular shaped segments over 1-month period. Comparable SNRs within 4% were observed for MLC moving and stationary plans on vendor-reconstructed images, and the direct k-space reconstructed images showed that the three SNRs are within 1%. The maximum leaf transmission for all three MLCs was less than 0.35% and the average leakage was 0.153 ± 0.006%, 0.151 ± 0.008%, and 0.159 ± 0.015% for head 1, 2, and 3, respectively. Both the leaf edge and leaf end penumbra showed comparable values within 0.05 cm, and the measured values are within 0.1 cm with TPS values. The leaf edge TG effect indicated 10% underdose and the leaf end TG showed a shifted dose distribution with 0.3 cm offset. The leaf positioning test showed a 0.2 cm accuracy in the PF style test, and a gamma passing rate above 96% was observed with a 3%/2 mm criteria when comparing the measured double/triple-rectangular pattern fluence with TPS calculated fluence. The average leaf speed when executing the test plan fell in a range from 1.86 to 1.95 cm/s. The measured and TPS calculated output factors were within 2% for squared fields and within 3% for rectangular fields. The reproducibility test showed the deviation of output factors were well within 2% for square fields and the gamma passing rate within 1.5% for fields with irregular segments. The Monte Carlo predicted output factors were within 2% compared to TPS values. 15 out of the 16 IMRT plans have gamma passing rate more than 98% compared to the TPS fluence with an average passing rate of 99.1 ± 0.6%. The MRIdian MLC has a good RF noise shielding design, low radiation leakage, good positioning accuracy, comparable TG effect, and can be modeled by an independent Monte Carlo calculation platform.

Intramuscular stimulation of tibialis anterior in human subjects: the effects of discharge variability on force production and fatigue

Continuous intramuscular stimulation of tibialis anterior (TA) was used to test the hypothesis that irregular trains of stimuli can increase force production and offset the magnitude of fatigue when compared with a continuous train of regular stimuli at an identical mean frequency (19 or 24 Hz). To achieve this, tungsten microelectrodes were inserted into the muscle belly into the motor point of the tibialis anterior muscle of able‐bodied individuals (aged 19–50) and stimulated at current intensities ranging from 5 to 7 mA. The motor point was stimulated with a continuous train of regular stimulation at either 19 or 24 Hz (n = 11) or until the force declined below 25% of the peak force at the onset of stimulation. For the first seven subjects, no fatigue was exhibited, and thus, we simply compared the forces generated by the regular and irregular segments of the continuous train (120 sec for each segment). For four additional subjects, we delivered a higher frequency train (24 Hz) that elicited some fatigue. Once the force had declined below 25% of the initial peak force (which took between 140 and 210 sec), the continuous irregular train was integrated. Interestingly, for those subjects who exhibited muscular fatigue, force always began to rise again once the irregularity was incorporated into the continuous regular train of stimulation at the identical mean frequency (24 Hz). We conclude that incorporating irregularity into continuous trains of stimuli offers a significant advantage to the human neuromuscular system during both fatigued and nonfatigued states and could offer benefits to therapies such as functional electrical stimulation (FES).

Fault‐Growth Pattern of the South Margin Normal Fault of the Yuguang Basin in Northwest Beijing and its Influencing Factors

Abstract:Based on high‐resolution remote sensing image interpretation, digital elevation model 3‐D analysis, field geologic field investigation, trenching engineering, and ground‐penetrating radar, synthetic research on the evolution of the Yuguang Basin South Margin Fault (YBSMF) in northwest Beijing was carried out. We found that the propagation and growth of faults most often occurred often at two locations: the fault overlapping zone and the uneven or rough fault segment. Through detailed observation and analysis of all cropouts of faults along the YBSMF from zone a to zone i, we identified three major factors that dominate or affect fault propagation and growth. First, the irregularity of fault geometry determine the propagation and growth of the fault, and therefore, the faults always propagate and grow at such irregular fault segments. The fault finally cuts off and eliminates its irregularity, making the fault geometry and fault plane smoother than before, which contributes to the slipping movement of the half‐graben block in the basin. Second, the scale of the irregularity of the fault geometry affects the result of fault propagation and growth, that is, the degree of the cutting off of fault irregularity. The degree of cutting off decreases as irregularity scale increases. Third, the maximum possible slip displacement of the fault segment influences the duration of fault propagation and growth. The duration at the central segments with a large slip displacement is longer than that at the end segments with a smaller slippage value.

Functional Analyses in the Silkworm,Bombyx mori, Support a Role for Notch Signaling in Appendage Development But Not theGroucho‐Dependent Pair‐Rule Process

Pair-rule genes are crucial for generating dual segment periodicity for body plan patterning in Drosophila. Bombyx mori is an intermediate germband insect, in which the formation of posterior segments via sequential addition follows a different process from that in Drosophila, although it is somewhat comparable to the process that occurs in vertebrates. Notch signaling is involved in the segmentation of vertebrates, spiders, and basal insects. Groucho (Gro) participates in Notch signaling as a corepressor and plays an important role during segmentation by interacting with other pair-rule proteins. Here, we cloned a gro homolog in the silkworm and positioned it at chromosome 21 in the genetic linkage map. Functional analyses of Bmgro and Bmnotch during embryogenesis were conducted using RNA interference (RNAi). Depletion of Bmgro led to a loss of odd-numbered segments, a characteristic pair-rule phenotype. Bmnotch RNAi resulted in that paired appendages on each segment were symmetrically fused along the ventral midline. An individual segment seemed to possess only one segmental appendage when Notch signaling was compromised. Irregular segments were observed in the Bmnotch RNAi embryo. Our results show that the involvement of Bmgro during the pair-rule process is not mediated by Notch signaling in silkworm. Notch signaling remains in appendage segmentation and restriction of cell fate.

Failure and behavior in water of hydroxyapatite whisker-reinforced bis-GMA-based resin composites

Failure mode under Hertzian indentation and the behavior on immersion in water of bis-GMA-based composites with HA whiskers or nanoscopic HA powder as filler were evaluated. Failure load decreased with increase in filler loading, but the decrease was smaller for whiskers, which showed a different failure mode both macroscopically and microscopically. Particle-filled composites failed mainly by radial cracking and cone cracking, with some plastic deformation at low filler loading, with fracture into irregular segments. For whisker-filled materials, crack propagation was inhibited by the well-dispersed whiskers by the usual toughening mechanisms; cone cracking was the dominant failure mode, at higher loads than for the powder, and fracture was incomplete. The filler reduced both water-uptake and elution of soluble materials, as expected, but both were lower for the whisker-filled material. Such composites might form the basis of viable materials for dental load-bearing restorations and other applications.

Fragmentation of coding region chromatin of trp-dioxygenase (to) and tyr-aminotransferase (tat) genes in their active and repressed states by micrococcal nuclease

The blot-hybridization technique-assisted we have studied the pattern of fragmentation by mirococcal nuclease (MNase) of DNA tyr-aminotransferase (tat) and trp-dioxygenase (to) genes in active (in rat cell liver nuclei) and repressed (in brain nuclei) states. It was provided, over a wide range of enzyme concentration two types of fragments are mainly produced: near full-size to- and tat-transcription unit (19,000 and 11,000 bp, respectively) and their large (from 1500 bp) heterogeneous in length. To-and tat-fragments of both kinds are preserved in hydrolyzates at limit of MNase digestion of total chromatin DNA when nuclease breaks occur in nearly all accessible sites of chromatin. This means that these fragments originate from two distinct subsets of transcription units coexistent in liver nuclei. The first of them do not contain MNase accessible sites over their entire length, whereas in other resistant regions alternate with rare irregular located MNase-sensitive segments. We presume that resistance to MNase within transcription units is peculiar to the competent genes. As a result of transcription MNase-sensitive areas arise which possibly flank elongating RNA polymerases.

Confocal microscopic evaluation of cornea after AquaLase liquefaction cataract extraction.

The most recent and innovative AquaLase liquefaction technology has offered an alternative to lens extraction. Many studies have investigated its functions and advantages. This article focuses on evaluating the in vivo microscopic cornea changes after AquaLase liquefaction by using a laser confocal microscope. In this perspective, randomized case study, 37 eyes of 35 patients submitted to cataract surgery were chosen to undergo AquaLase liquefaction cataract extraction. Each patient was assessed before the operation, on the 1(st), 7(th), and 30(th) postoperative days, and 6 months after the cataract extraction. The morphologies and quantitative comparisons of corneal cells and corneal nerves layer by layer were evaluated in vivo with the Heidelberg Retina Tomograph III-Rostock Cornea Module (HRT-III RCM) confocal microscope. ANOVA and Post-Hoc Bonferroni test were carried out to compare the results pre- and post-operation. ANOVA results indicated no post-operation changes for epithelium and anterior stroma cells. Irregular segments of sub-basal nerve fiber were most pronounced seven days post-operation. In the mid and posterior stroma, keratocytes were obvious compared with the preoperative condition. Corneal endothelium cells became obviously swollen in cytoplasm and nucleus. The mid and posterior stroma cell density decreased from the 1(st) to 7(th) postoperative days (P<0.05). The corneal endothelium cell density decreased (P<0.05) and did not revert to the preoperative level after six months (P<0.05). Slight microstructural abnormalities were identified in the corneal recovery process after AquaLase liquefaction. AquaLase liquefaction cataract extraction is safe for cornea.

Does Stacking Restrain the Photodynamics of Individual Nucleobases?

Nonadiabatic photodynamical simulations of 4-aminopyrimidine (4-APy) used as a model for adenine were performed by embedding it between two stacking methyl-guanine (mGua) molecules to determine the effect of spatial restrictions on the ultrafast photodeactivation mechanism of this nucleobase. A hybrid multiconfigurational ab initio/molecular mechanical approach in combination with surface hopping was used. During the dynamics the formation of a significant fraction of intrastrand hydrogen bonding from 4-APy to mGua above and below is observed. These findings show that this type of hydrogen bond may play an important role for the photodynamics within one DNA strand and that it should be of interest even in irregular segments of double stranded nucleic acids structures. The relaxation mechanism of internal conversion to the ground state is dominated by ring puckering, and an overall elongation of the lifetime of the embedded system by approximately 20% as compared to the isolated 4-APy is computed.