1,503 research outputs found
Hydrodynamics of Diatom Chains and Semiflexible Fibres
Diatoms are non-motile, unicellular phytoplankton that have the ability to form colonies in the form of chains. Depending upon the species of diatoms and the linking structures that hold the cells together, these chains can be quite stiff or very flexible. Recently, the bending rigidities of some species of diatom chains have been quantified. In an effort to understand the role of flexibility in nutrient uptake and aggregate formation, we begin by developing a three-dimensional model of the coupled elastic-hydrodynamic system of a diatom chain moving in an incompressible fluid. We find that simple beam theory does a good job of describing diatom chain deformation in a parabolic flow when its ends are tethered, but does not tell the whole story of chain deformations when they are subjected to compressive stresses in shear. While motivated by the fluid dynamics of diatom chains, our computational model of semiflexible fibres illustrates features that apply widely to other systems. The use of an adaptive immersed boundary framework allows us to capture complicated buckling and recovery dynamics of long, semiflexible fibres in shear
A Toy Model of Flying Snake's Glide
We have developed a toy model of flying snake's glide [J.J. Socha, Nature
vol. 418 (2002) 603.] by modifying a model for a falling paper. We have found
that asymmetric oscillation is a key about why snake can glide. Further
investigation for snake's glide will provide us details about how it can glide
without a wing.Comment: 6 pages, to be submitted to J. Phys. Soc. Jpn. Revised Version
submitted to the abov
Hydrodynamic phase-locking of swimming microorganisms
Some microorganisms, such as spermatozoa, synchronize their flagella when
swimming in close proximity. Using a simplified model (two infinite, parallel,
two-dimensional waving sheets), we show that phase-locking arises from
hydrodynamics forces alone, and has its origin in the front-back asymmetry of
the geometry of their flagellar waveform. The time-evolution of the phase
difference between co-swimming cells depends only on the nature of this
geometrical asymmetry, and microorganisms can phase-lock into conformations
which minimize or maximize energy dissipation
Cooperation of Sperm in Two Dimensions: Synchronization, Attraction and Aggregation through Hydrodynamic Interactions
Sperm swimming at low Reynolds number have strong hydrodynamic interactions
when their concentration is high in vivo or near substrates in vitro. The
beating tails not only propel the sperm through a fluid, but also create flow
fields through which sperm interact with each other. We study the hydrodynamic
interaction and cooperation of sperm embedded in a two-dimensional fluid by
using a particle-based mesoscopic simulation method, multi-particle collision
dynamics (MPC). We analyze the sperm behavior by investigating the relationship
between the beating-phase difference and the relative sperm position, as well
as the energy consumption. Two effects of hydrodynamic interaction are found,
synchronization and attraction. With these hydrodynamic effects, a multi-sperm
system shows swarm behavior with a power-law dependence of the average cluster
size on the width of the distribution of beating frequencies
Effects of Cell Morphology and Attachment to a Surface on the Hydrodynamic Performance of Unicellular Choanoflagellates
Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, are closely related to animals and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta has a complex life cycle with different morphotypes, some unicellular and some multicellular. Here we use computational fluid dynamics to study the hydrodynamics of swimming and feeding by different unicellular stages of S. rosetta: a swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum, a thecate cell attached to a surface and a dispersal-stage cell with a slender body, long flagellum and short collar. We show that a longer flagellum increases swimming speed, longer microvilli reduce speed and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. We show that ignoring the collar, as earlier models have done, overestimates flux and greatly overestimates the benefit to feeding performance of swimming versus being attached, and of a longer stalk for attached cells
Study on hepatitis B and C serologic status among municipal solid waste workers in Messina (Italy)
A study on hepatitis B and C virus seroprevalence was carried out on blood samples from 327 municipal solid waste workers in Messina (Italy) to verify the hypothesis that this category of workers is at high risk for such diseases. The fact that 32.41% of all the subjects showed previous exposure to hepatitis B virus (HBV) substantiates the need to proceed with compulsory HBV vaccine prophylaxis in this category of workers, also in anticipation of possible medical legal litigations
Identification of the microorganisms responsible for periodontopathy by Multiplex RT-PCR
The aim of our research was to identify by bacterial genomicDNA analysis the prevalence of five different species of periodontopathogenic bacteria present in the subgingival biofilm,specifically: Actinobacillus actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg), Prevotella intermedia (Pi), Bacterioides forsytus (Bf), Treponema denticola (Td).For the analysis we used the systematic Multiplex-PCR-microdentkit with species-specific primers. We studied a group of 48 subjects, 18 males and 30 females, from 18 to 78 years of age. Theinitial clinical screening enabled us to select, among the groupanalysed, 24 subjects with signs of active periodontopathy (GroupA) and 24 patients without identifiable clinical evidence of the disease used as the control group (Group B). Within the two experimental groups (A and B), the test was found to be positive in 75%of subjects from group A, whereas the test was found to be negative in all the subjects from group B. Our research shows thatthe Multiplex-PCR system is reliable. Furthermore, the sensitivity and simplicity of this technique, as well as the decrease inworking times and the possibility of identifying non-culturablebacteria, since the presence of viable organisms is not essential,make this technique indicated for the simultaneous identificationof periodontopathogenic bacteria and might, in perspective, pro-vide a more effective clinical alternative to the techniques of bacterial typing of the subgingival plaque
Design and proof-of-concept of an advanced protective system for the dissipation of tangential impact energy in helmets, based on non-Newtonian fluids
A Computer Aided Detection system for mammographic images implemented on a GRID infrastructure
The use of an automatic system for the analysis of mammographic images has
proven to be very useful to radiologists in the investigation of breast cancer,
especially in the framework of mammographic-screening programs. A breast
neoplasia is often marked by the presence of microcalcification clusters and
massive lesions in the mammogram: hence the need for tools able to recognize
such lesions at an early stage. In the framework of the GPCALMA (GRID Platform
for Computer Assisted Library for MAmmography) project, the co-working of
italian physicists and radiologists built a large distributed database of
digitized mammographic images (about 5500 images corresponding to 1650
patients) and developed a CAD (Computer Aided Detection) system, able to make
an automatic search of massive lesions and microcalcification clusters. The CAD
is implemented in the GPCALMA integrated station, which can be used also for
digitization, as archive and to perform statistical analyses. Some GPCALMA
integrated stations have already been implemented and are currently on clinical
trial in some italian hospitals. The emerging GRID technology can been used to
connect the GPCALMA integrated stations operating in different medical centers.
The GRID approach will support an effective tele- and co-working between
radiologists, cancer specialists and epidemiology experts by allowing remote
image analysis and interactive online diagnosis.Comment: 5 pages, 5 figures, to appear in the Proceedings of the 13th
IEEE-NPSS Real Time Conference 2003, Montreal, Canada, May 18-23 200
Portable CdTe detection system for mammographic X-ray spectroscopy
This paper describes a portable apparatus to be utilized in mammographic X-ray spectroscopy under clinical conditions. The system, based on a CdTe solid-state detector, is able to directly measure mammographic X-ray tube spectra. Good system response to monoenergetic photons was measured using X-ray and γ-ray calibration sources (109Cd and 241Am). The measured molybdenum X-ray spectra, in agreement with simulated spectra, show the good spectral capability of the system also at high photon fluence rates, as typical of clinical mammography. Low tailing, no secondary X-ray escape and low pile-up distortions in the measured spectra indicate that this portable system is suitable for mammographic X-ray spectroscopy
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