scholarly journals CHROMOSOME VELOCITY DURING MITOSIS AS A FUNCTION OF CHROMOSOME SIZE AND POSITION

1965 ◽  
Vol 25 (1) ◽  
pp. 119-135 ◽  
Author(s):  
R. Bruce Nicklas
Keyword(s):  
Mechanical Model ◽  
Phase Contrast ◽  
Frictional Resistance ◽  
Small Chromosome ◽  
Chromosome Size ◽  
Size Dependent ◽  
Significant Difference ◽  
Melanoplus Differentialis ◽  
X Irradiation ◽  
Molecular Origin

Chromosome velocity has been studied in living Melanoplus differentialis spermatocytes by phase contrast cinemicrography. Melanoplus chromosomes (and bivalents) differ in length by as much as 1:3.5. As expected, no size-dependent velocity differences were detected in anaphase, and this is also shown to be true for the less predictable movements during prometaphase congression. The size of the X chromosome can change during observation following x-irradiation, but this is equally without influence on velocity. However, an effect of position on velocity is found in both prometaphase and in anaphase: the chromosomes furthest from the central interpolar axis move 25 per cent faster than more central chromosomes. A simple mechanical model relating frictional resistance and mitotic forces to chromosome velocity is discussed in detail. Calculations from the model suggest that a significant difference in the force acting on a large, as compared with a small chromosome is necessary to account for the observed similarity in velocity. Therefore, it is concluded that the mitotic forces are so organized or regulated that velocity is, within limits, independent of load. The implications of velocity-load independence in relation to the molecular origin of mitotic forces are discussed.

Chromosome size-dependent control of meiotic recombination

Science ◽  
1992 ◽  
Vol 256 (5054) ◽  
pp. 228-232 ◽  
Author(s):  
D. Kaback ◽  
V Guacci ◽  
D Barber ◽  
J. Mahon
Keyword(s):  
Meiotic Recombination ◽  
Chromosome Size ◽  
Size Dependent

scholarly journals Frictional Characteristics of the Newer Low-friction Elastomeric Ligatures

2016 ◽  
Vol 6 (1) ◽  
pp. 19-23
Author(s):  
Amol Mhatre ◽  
VK Ravindranath ◽  
Sachin Doshi ◽  
Girish Karandikar ◽  
PS Vivek
Keyword(s):  
Testing Machine ◽  
Frictional Resistance ◽  
Minimal Amount ◽  
New Delhi ◽  
Low Friction ◽  
Significant Difference ◽  
Group A ◽  
Group B ◽  
New Generation

ABSTRACT Aim The aim of this in vitro study was to investigate the efficiency of the new generation of elastomeric ligatures with innovative designs (SlideTM and AlastiKTM Easy-to-Tie) in reducing frictional resistance (FR) during sliding mechanics as compared with conventional ligatures. Materials and Methods Sixty ligature samples divided into four groups were used for the study. Group A: QuiK-StiK™ (3M Unitek, Monrovia, CA, USA), Group B: AlastiK™ Easy-to-Tie (3M Unitek, Monrovia, CA, USA), Group C: Slide™ (Leone, Firenze, Italy), and Group D: SS ligatures 0.010” (Libral Traders, New Delhi, India). Universal Testing Machine, Instron was used for measuring FR at the bracket-wire interface. Results There was statistically significant difference in FR among all the four groups of ligatures tested (p < 0.001). Slide ligatures produced the least amount of FR followed by SS ligatures, Easy-to-Tie, and QuiK-StiK in the increasing order of the FR values registered. Conclusion SlideTM ligatures may represent a valid alternative to passive self-ligating brackets when minimal amount of friction is desired. Angulation introduced into the elastomeric ligatures reduces the friction in comparison to conventional elastomeric ligatures. How to cite this article Vivek PS, Ravindranath VK, Karandikar G, Doshi S, Mhatre A, Sonawane M. Frictional Characteristics of the Newer Low-friction Elastomeric Ligatures. J Contemp Dent 2016;6(1):19-23.

P5280The impact of background phase offset errors in cardiovascular magnetic resonance phase contrast imaging: a multi-scanner study

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
S C S Minderhoud ◽  
N Van Der Velde ◽  
J J Wentzel ◽  
M Attrach ◽  
P A Wielopolski ◽  
...  
Keyword(s):  
Phase Contrast ◽  
Main Pulmonary Artery ◽  
Flow Quantification ◽  
Flow Measurements ◽  
Total N ◽  
Phase Offset ◽  
Wide Range ◽  
Significant Difference ◽  
Clinically Significant ◽  
The Impact

Abstract Background Phase contrast (PC) CMR flow measurements (FM) are widely used for blood flow assessment, but they suffer from phase offset errors (POE). Stationary phantom correction limits these inaccuracies, however, this adds scan time. Stationary tissue (ST) correction is an alternative method that does not require additional scanning. The aim of this study was to evaluate the impact of POE, to assess interscanner variation, and to evaluate the ST correction usage. Methods We included 166 patients in which both aorta and main pulmonary artery FM were acquired including static gelatin phantom data. Subjects were scanned on three types of 1.5T scanners from the one vendor. Uncorrected and ST corrected FM were compared with phantom corrected FM, our reference value, and corrected for BSA. A difference of >10% in net flow was defined as clinically relevant. Regurgitation fraction was calculated and POE influences were assessed. Regurgitation severity was graded and POE influence on severity grading was assessed. Results Of the 166 cases included, the median age was 27 (5–74) years. Overall, the median difference between no corrected and phantom corrected FM was ≤6%, however, with a wide range of over- and underestimation (−155%–78% change) (figure). ST correction resulted in larger differences compared to no correction (p<0.01). Clinically significant differences were seen in 19% of all FM with no correction and in 30% of with ST correction (p<0.01). Furthermore, there were significant differences between scanners (no correction 10%, p<0.01; ST correction, p<0.01). Regurgitation severity indexing changed in 38 (11%) cases with no correction and in 48 (48%) with ST correction. Magnitude of flow change with and without offset corrections (n=332) Flow (ml/m2) Δ no correction and phantom correction (%) Δ ST correction and phantom correction (%) Clinically significant difference (>10%) Mean ± SD Median IQR Range Median IQR Range No correction, N (%) ST correction , N (%) MRI 1 (n=126) 50±12 3 0 to 6 −8 to 30 5 −3 to 9 −26 to 28 13 (10%) 34 (27%) MRI 2 (n=102) 48±13 −2 −15 to 6 −155 to 78 5 −3 to 11 −74 to 52 50 (49%) 50 (49%) MRI 3 (n=104) 48±12 −1 −1 to 0 −7 to 14 2 −2 to 5 −39 to 29 1 (1%) 16 (15%) Total (n=332) 49±12 0 −2 to 4 −155 to 78 3 −2 to 8 −74 to 52 64 (19%) 100 (30%) Conclusion Background POE have a significant impact on flow quantification and regurgitation severity. Unexpectedly, background correction using ST correction worsens accuracy compared to no correction. POE vary greatly between scanners. Therefore, careful assessment of FM at each scanner is essential to determine if routine phantom scanning is necessary.

scholarly journals Cine Phase-Contrast MR Images Failed to Predict Clinical Outcome Following ETV

2009 ◽  
Vol 36 (5) ◽  
pp. 643-647 ◽  
Author(s):  
Xiao Di ◽  
M. Ragab ◽  
Mark G. Luciano
Keyword(s):  
Brain Stem ◽  
Phase Contrast ◽  
Obstructive Hydrocephalus ◽  
Dynamic Mri ◽  
Magnetic Resonance Images ◽  
Third Ventriculostomy ◽  
Coronal Image ◽  
Significant Difference ◽  
The Brain ◽  
Basal Cisterns

Background:To predict success of endoscopic third ventriculostomy (ETV) in patients with obstructive hydrocephalus, we evaluated pre- and post- operative phase-contrast cine magnetic resonance images (PC MRI) on cerebrospinal fluid (CSF), cine flow in basal cisterns around the brain stem, and cervical medullar junction (CMJ) retrospectively.Methods:The study involved 102 patients with mean age of 36.74±23.25, and F/M = 1.55. All patients had PC MRI taken both pre- and post-operatively. A dynamic MRI video of PC MRI was reviewed at sagittal, axial, and coronal sections to determine cistern flows around the brain stem and CMJ. For quantitative analysis, quadrants were divided around midbrain axially to evaluate interpeduncular, quadrageminal, and ambient cisterns of both sides using scores of 0 to 60. Pre- and post- pontine and CMJ flows were shown in sagittal view and scored 0 to 20, and lateral cerebellopontine cisterns of both sides were measured on coronal image and scored 0 to 20.Results:No significant difference in CSF flow was seen from three individual views and total cine score, or between ETV success and failure groups by multivariate analysis of variance. Kaplan-Meier Analysis and Spearman's Correlation Test produced no relationship between MRI cine flow scores and interval period after surgery to ETV failure.Conclusion:PC MRI cine flow failed to demonstrate significant differences between successful and failed ETV groups. This indicates in addition to achieving an adequate fenestration, CSF pathways beyond the basal cisterns around the brain stem and CMJ may play an essential role in achieving ETV success.

Nanoindentation hardness of a Steigmann–Ogden surface bounding an elastic half-space

2018 ◽  
Vol 24 (9) ◽  
pp. 2754-2766 ◽  
Author(s):  
Xiaobao Li ◽  
Changwen Mi
Keyword(s):  
Surface Tension ◽  
Half Space ◽  
Surface Elasticity ◽  
Elastic Half Space ◽  
Indentation Hardness ◽  
Bending Rigidity ◽  
Size Dependent ◽  
Significant Difference ◽  
Nanoindentation Hardness ◽  
Membrane Stiffness

Previous studies demonstrate that, for nanostructures under transverse bending, the effective Young modulus is appreciably greater (in magnitude) than that of the same elements under axial loads. Therefore, in addition to the conventional residual surface tension and membrane stiffness, the curvature dependence of surface energy is desired for inhomogeneously strained nanostructures. In this paper, we aim to reevaluate the size-dependent nanoindentation hardness of an elastic half-space subjected to nanosized frictionless traction, through the use of both the curvature-independent Gurtin–Murdoch and the curvature-dependent Steigmann–Ogden models of surface elasticity. The nanoindentation problem is solved by the integration of Boussinesq’s method of displacement potentials and Hankel integral transforms. As examples, the effects of residual surface tension, membrane stiffness, and bending rigidity of the half-space boundary are parametrically analyzed in detail for a uniform circular pressure and a concentrated normal force. The observations in semianalytical calculations suggest a significant difference in the nanoindentation hardnesses predicted from the two popular models of surface mechanics. In most cases, the inclusion of bending rigidity results in smaller displacements and stresses, and therefore higher indentation hardness. Based on physically interpretable numerical values of surface material properties, we show that a curvature-dependent model of surface elasticity is required in order to characterize the size-dependent feature of nanoindentation problems correctly.

scholarly journals Fold-Over Oversampling Effects in the Measurements of Cerebral Cerebrospinal Fluid and Blood Flows with 2D Cine Phase-Contrast MRI

Diagnostics ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 387
Author(s):  
Fadoua Saadani-Makki ◽  
Serge Metanbou ◽  
Garance Arbeaumont-Trocme ◽  
Julien Van Gysel ◽  
Malek I. Makki
Keyword(s):  
Blood Flow ◽  
Cerebrospinal Fluid ◽  
Stroke Volume ◽  
Phase Contrast ◽  
Blood Flows ◽  
Phase Offset ◽  
Section Area ◽  
Significant Difference ◽  
Before And After ◽  
Cine Phase Contrast

This prospective study investigated the effects of fold-over oversampling on phase-offset background errors with 2D-Cine phase contrast (Cine-PC) magnetic resonance imaging (MRI). It was performed on brain MRI and compared to conventional Full-field of view FOV coverage and it was tested with two different velocity encoding (Venc) values. We chose Venc = 100 mm/s to encode cerebrospinal fluid (CSF) flows in the aqueduct and 600 mm/s to encode blood flow in the carotid artery. Cine-PC was carried out on 10 healthy adult volunteers followed simultaneously by an acquisition on static agar-gel phantom to measure the phase-offset background errors. Pixel-wise correction of both the CSF and the blood flows was calculated through 32 points of the cardiac-cycle. We compared the velocity-to-noise ratio, the section area, the absolute and the corrected velocity (peak; mean and minimum), the net flow, and the stroke volume before and after correction. We performed the statistical T-test to compare Full-FOV and fold-over and Bland–Altman plots to analyze their differences. Our results showed that following phase-offset error correction, the blood stroke-volume was significantly higher with Full-FOV compared to fold-over. We observed a significantly higher CSF mean velocity and net flow values in the fold-over option. Compared to Full-FOV, fold-over provides a significantly larger section area and significantly lower peak velocity-offset in the aqueduct. No significant difference between the two coverages was reported before and after phase-offset in blood flow measurements. In conclusion, fold-over oversampling can be chosen as an alternative to increase spatial resolution and accurate cerebral flow quantification in Cine-PC.

scholarly journals The cytology of Aspergillus nidulans

1960 ◽  
Vol 1 (3) ◽  
pp. 462-476 ◽  
Author(s):  
Charles G. Elliott
Keyword(s):  
Aspergillus Nidulans ◽  
Small Chromosome ◽  
Chromosome 8 ◽  
Chromosome 6 ◽  
Normal Strain ◽  
Chromosome 2 ◽  
Small Fragment ◽  
Zygote Nucleus ◽  
Dense Cytoplasm ◽  
X Irradiation

In haploid strains of Aspergillus nidulans, asci arise from croziers. The two nuclei of the young ascus (the penultimate cell of the crozier) fuse, and the zygote nucleus immediately undergoes meiosis. At diakinesis and first metaphase eight bivalents are seen: three large (one, Chromosome 2, with a satellite), two medium sized (Chromosomes 4 and 5), two small (Chromosomes 6 and 7) and one very small (Chromosome 8). The perithecia of haploid strains are packed with asci and have very few sterile hyphae.Diploid strains (heterozygotes made by Roper's technique) are very different from haploids in that the perithecia contain many sterile hyphae with little cytoplasm and coiled hyphae with dense cytoplasm made up mainly of uninucleate cells, and there are few asci in a perithecium. Croziers are absent: some of the cells of the coiled hyphae become asci. At diakinesis and first metaphase, the same chromosome configurations are seen as in a cross between the haploid strains from which the diploid was synthesized; the chromosomes are bivalents. The young ascus thus has a single (diploid) nucleus which undergoes meiosis, and asci develop apogamously. No evidence of nuclear fusion in the young ascus and of a tetraploid meiosis was obtained. Cultures from ascopores isolated by micro-manipulation from perithecia of diploids were all haploid. Meiosis appears to proceed normally to first metaphase, but typical later stages, and asci with spores, are rarely seen. First anaphase frequently fails to occur, and the chromosomes clump together.In the strain ad2 y, obtained from a normal strain by X-irradiation, nine bivalents are present, one a very small fragment. In crosses between ad2 y and a normal strain, and in a diploid made from them, the fragment pairs with Chromosome 6. Asci in the cross between ad2 y and a normal haploid are highly irregular, often with less than the usual eight spores.

Quantum-mechanical model for phase-contrast imaging of non-crystalline objects

2016 ◽  
Vol 47 (2-3) ◽  
pp. 246-253 ◽  
Author(s):  
V. B. Molodkin ◽  
G. O. Velikhovskii ◽  
S. V. Lizunova ◽  
V. V. Lizunov ◽  
B. V. Sheludchenko ◽  
...  
Keyword(s):  
Mechanical Model ◽  
Phase Contrast ◽  
Phase Contrast Imaging ◽  
Quantum Mechanical ◽  
Contrast Imaging ◽  
Quantum Mechanical Model
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